Several rads just haven't always been getting hot when the timer
switches the central heating and hot water on and it's been driving me
nuts.
On 14/12/2024 18:57, eastender wrote:
Several rads just haven't always been getting hot when the timer
switches the central heating and hot water on and it's been driving me nuts.
What is 'havent always been getting hot' mean?
What temperature are they getting to?
Be aware, most humans cannot detect temperature above around 47 deg. C,
it just hurts beyond that, so there is no way a (normal) human can
detect a difference between rads at 55 and 65 degrees.
And what temerature are the others getting to?
Is the auto bypass set too weak, so it lets the heated water back
through before it hits the rads?
The boiler will be putting out the same temperature heated water whether
the HW or CH was on, its only if the cylinder coil was absorbing more
heat than the CH system , that the flow temperature to the CH would be
lower, even then, its doubtful that could happen, as they are S valves,
so the same amount of water should, in theory, be pushed around the
system, but if the HW circuit is smaller, and the cylinder water needs heating, then that could take the bulk of the heated water, thus
reducing radiator temperatures.
Why is the HW on? Dont you have 2 set times each day for it? Having it
set on, with the cylinder stat calling for heat whenever it drops a
degree or so is quite inefficient, the boiler will be firing up for
short periods regularly if that is the way it is set.
eastender <user150@newsgrouper.org.uk.invalid> wrote:
Several rads just haven't always been getting hot when the timer switches the central heating and hot water on and it's been driving me nuts.
It's a standard S-plan unvented system boiler arrangement with two motorised valves, one for each circuit, but with a lot of rads – 17 – and
an unvented hot water tank. I thought it was air blocks and/or balancing
so have been running around bleeding and adjusting the lock valves but nothing worked.
Anyway today I had the brainwave of switching the hot water off and
leaving the heating on and lo and behold the rads all came to life. What’s likely to be the reason? The hot water tank has a thermostat so I would have thought it should close the valve but maybe it isn’t and is causing a pressure issue of some sort.
Have a look at your pump speed settings (if any). It may be that your pump
is failing and doesn’t have enough “oomph” to push water around your HW tank and CH circuit simultaneously.
You may get away with turning your pump speed up but if it is failing, a replacement may be on the cards.
Tim
Tim+ <timdownieuk@yahoo.co.youkay> posted:
eastender <user150@newsgrouper.org.uk.invalid> wrote:
Several rads just haven't always been getting hot when the timer switches >>> the central heating and hot water on and it's been driving me nuts.
It's a standard S-plan unvented system boiler arrangement with two
motorised valves, one for each circuit, but with a lot of rads – 17 – and
an unvented hot water tank. I thought it was air blocks and/or balancing >>> so have been running around bleeding and adjusting the lock valves but nothing worked.
Anyway today I had the brainwave of switching the hot water off and
leaving the heating on and lo and behold the rads all came to life.
What’s likely to be the reason? The hot water tank has a thermostat so I >>> would have thought it should close the valve but maybe it isn’t and is >>> causing a pressure issue of some sort.
Have a look at your pump speed settings (if any). It may be that your pump >> is failing and doesn’t have enough “oomph” to push water around your HW
tank and CH circuit simultaneously.
You may get away with turning your pump speed up but if it is failing, a
replacement may be on the cards.
Tim
The boiler - a Vaillant EcoTec Plus - is only 3 years old but we have a warranty service scheduled so will ask the tech to look at the oomph setting.
On 15/12/2024 11:55, eastender wrote:
Tim+ <timdownieuk@yahoo.co.youkay> posted:
eastender <user150@newsgrouper.org.uk.invalid> wrote:
Several rads just haven't always been getting hot when the timer
switches
the central heating and hot water on and it's been driving me nuts.
It's a standard S-plan unvented system boiler arrangement with two
motorised valves, one for each circuit, but with a lot of rads – 17
– and
an unvented hot water tank. I thought it was air blocks and/or
balancing
so have been running around bleeding and adjusting the lock valves
but nothing worked.
Anyway today I had the brainwave of switching the hot water off and
leaving the heating on and lo and behold the rads all came to life.
What’s likely to be the reason? The hot water tank has a thermostat
so I
would have thought it should close the valve but maybe it isn’t and is >>>> causing a pressure issue of some sort.
Have a look at your pump speed settings (if any). It may be that your
pump
is failing and doesn’t have enough “oomph” to push water around your HW
tank and CH circuit simultaneously.
You may get away with turning your pump speed up but if it is failing, a >>> replacement may be on the cards.
Tim
The boiler - a Vaillant EcoTec Plus - is only 3 years old but we have
a warranty service scheduled so will ask the tech to look at the oomph
setting.
What temperature is the cylinder stat set to?
Several rads just haven't always been getting hot when the timer switches
the central heating and hot water on and it's been driving me nuts.
It's a standard S-plan unvented system boiler arrangement with two
motorised valves, one for each circuit, but with a lot of rads – 17 – and an unvented hot water tank. I thought it was air blocks and/or balancing
so have been running around bleeding and adjusting the lock valves but nothing worked.
Anyway today I had the brainwave of switching the hot water off and
leaving the heating on and lo and behold the rads all came to life.
What’s likely to be the reason? The hot water tank has a thermostat so I would have thought it should close the valve but maybe it isn’t and is causing a pressure issue of some sort.
Several rads just haven't always been getting hot when the timer
switches the central heating and hot water on and it's been driving
me nuts. It's a standard S-plan unvented system boiler arrangement
with two motorised valves, one for each circuit, but with a lot of
rads – 17 – and an unvented hot water tank. I thought it was air
blocks and/or balancing so have been running around bleeding and
adjusting the lock valves but nothing worked. Anyway today I had the brainwave of switching the hot water off and leaving the heating on
and lo and behold the rads all came to life. What’s likely to be the reason? The hot water tank has a thermostat so I would have thought
it should close the valve but maybe it isn’t and is causing a
pressure issue of some sort.
eastender <user150@newsgrouper.org.uk.invalid> wrote:
Several rads just haven't always been getting hot when the timer switches
the central heating and hot water on and it's been driving me nuts.
It's a standard S-plan unvented system boiler arrangement with two
motorised valves, one for each circuit, but with a lot of rads – 17 – and
an unvented hot water tank. I thought it was air blocks and/or balancing
so have been running around bleeding and adjusting the lock valves but nothing worked.
Anyway today I had the brainwave of switching the hot water off and
leaving the heating on and lo and behold the rads all came to life.
What’s likely to be the reason? The hot water tank has a thermostat so I >> would have thought it should close the valve but maybe it isn’t and is
causing a pressure issue of some sort.
Have a look at your pump speed settings (if any). It may be that your pump
is failing and doesn’t have enough “oomph” to push water around your HW tank and CH circuit simultaneously.
Tim+ <timdownieuk@yahoo.co.youkay> posted:
eastender <user150@newsgrouper.org.uk.invalid> wrote:
Several rads just haven't always been getting hot when the timerHave a look at your pump speed settings (if any). It may be that your
switches the central heating and hot water on and it's been driving
me nuts.
It's a standard S-plan unvented system boiler arrangement with two
motorised valves, one for each circuit, but with a lot of rads – 17 – >> > and an unvented hot water tank. I thought it was air blocks and/or
balancing so have been running around bleeding and adjusting the lock
valves but nothing worked.
Anyway today I had the brainwave of switching the hot water off and
leaving the heating on and lo and behold the rads all came to life.
What’s likely to be the reason? The hot water tank has a thermostat
so I would have thought it should close the valve but maybe it isn’t
and is causing a pressure issue of some sort.
pump is failing and doesn’t have enough “oomph” to push water around >> your HW tank and CH circuit simultaneously.
You may get away with turning your pump speed up but if it is failing,
a replacement may be on the cards.
Tim
The boiler - a Vaillant EcoTec Plus - is only 3 years old but we have a warranty service scheduled so will ask the tech to look at the oomph
setting.
On Sun, 15 Dec 2024 11:55:58 GMT, eastender wrote:
The boiler - a Vaillant EcoTec Plus - is only 3 years old but we have a
warranty service scheduled so will ask the tech to look at the oomph
setting.
The software on these boilers is utter shit and cannot be fixed by
adjusting the settings. I know, I have one.
On Sun, 15 Dec 2024 11:55:58 GMT, eastender wrote:
Tim+ <timdownieuk@yahoo.co.youkay> posted:
eastender <user150@newsgrouper.org.uk.invalid> wrote:
Several rads just haven't always been getting hot when the timerHave a look at your pump speed settings (if any). It may be that your
switches the central heating and hot water on and it's been driving
me nuts.
It's a standard S-plan unvented system boiler arrangement with two
motorised valves, one for each circuit, but with a lot of rads – 17 – >>>> and an unvented hot water tank. I thought it was air blocks and/or
balancing so have been running around bleeding and adjusting the lock
valves but nothing worked.
Anyway today I had the brainwave of switching the hot water off and
leaving the heating on and lo and behold the rads all came to life.
What’s likely to be the reason? The hot water tank has a thermostat
so I would have thought it should close the valve but maybe it isn’t >>>> and is causing a pressure issue of some sort.
pump is failing and doesn’t have enough “oomph” to push water around >>> your HW tank and CH circuit simultaneously.
You may get away with turning your pump speed up but if it is failing,
a replacement may be on the cards.
Tim
The boiler - a Vaillant EcoTec Plus - is only 3 years old but we have a
warranty service scheduled so will ask the tech to look at the oomph
setting.
The software on these boilers is utter shit and cannot be fixed by
adjusting the settings. I know, I have one.
On 14/12/2024 18:57, eastender wrote:
Several rads just haven't always been getting hot when the timer
switches the central heating and hot water on and it's been driving
me nuts. It's a standard S-plan unvented system boiler arrangement
with two motorised valves, one for each circuit, but with a lot of
rads – 17 – and an unvented hot water tank. I thought it was air
So one heating zone and one DHW zone?
blocks and/or balancing so have been running around bleeding and
adjusting the lock valves but nothing worked. Anyway today I had the brainwave of switching the hot water off and leaving the heating on
and lo and behold the rads all came to life. What’s likely to be the reason? The hot water tank has a thermostat so I would have thought
it should close the valve but maybe it isn’t and is causing a
pressure issue of some sort.
Chances are the DHW loop has significantly less flow resistance than the
CH circuit, so with both zone valves open, you may get the bulk of the
flow through the DHW circuit. Even if the cylinder is up to temp, it
could still divert flow from the rads.
Much depends on how the system is setup. Ideally you want the DHW zone
to close when the cylinder is at or reaches set point temp.
Since it is probably a very fast recovery cylinder that can absorb close
to the full output of the boiler, operating in DHW priority mode might
make more sense - schedule DHW reheat at times the CH is not on. You
might also find that your boiler is capable of split temperature
operation - i.e. where the boiler knows when it is heating DHW rather
than CH, and can run different flow temperatures. This allows you to get better condensing efficiency in the less heating intensive months since
the rads can run cooler, but the DHW is still heated to an adequate temperature to ensure sanitisation of the water.
You could also take that further and use full weather compensation:
https://wiki.diyfaq.org.uk/index.php/Weather_compensation
If you really want to run both zones at once on a regular basis, then
adding a manual balancing valve into the DHW primary loop would help -
then you could balance the cylinder with the rads so that it can't rob
them of flow.
Details on S plan configuration here:
https://wiki.diyfaq.org.uk/index.php/Central_Heating_Controls_and_Zoning#CH_and_DHW_zones:_S-plan
On 15/12/2024 11:25, Tim+ wrote:
eastender <user150@newsgrouper.org.uk.invalid> wrote:
Several rads just haven't always been getting hot when the timer switches >> the central heating and hot water on and it's been driving me nuts.
It's a standard S-plan unvented system boiler arrangement with two
motorised valves, one for each circuit, but with a lot of rads – 17 – and
an unvented hot water tank. I thought it was air blocks and/or balancing >> so have been running around bleeding and adjusting the lock valves but nothing worked.
Anyway today I had the brainwave of switching the hot water off and
leaving the heating on and lo and behold the rads all came to life.
What’s likely to be the reason? The hot water tank has a thermostat so I >> would have thought it should close the valve but maybe it isn’t and is >> causing a pressure issue of some sort.
Have a look at your pump speed settings (if any). It may be that your pump is failing and doesn’t have enough “oomph” to push water around your HW
tank and CH circuit simultaneously.
Water will always take the path of least resistance which in this case
is likely to be the path through the hot water tank. Pushing up the pump oomph will not necessarily solve the problem.
What also could be happening is that most of the water is circulating
through the hot water tank coils and at speed that return temperature to
the boiler rises close to the flow temperature. The boiler can only
modulate down so far and with a high return temperature it has to cut
off or else the flow exceeds the configured flow temperature. To prevent short cycling the Vaillant EcoTec Plus will now inhibit the burner
firing for perhaps 5 minutes. During this 5 minute period the flow and
return temperature may drop by 10C or more. The lesser amount of water flowing through the radiators will now be cooler.
Once the hot water has reached the correct temperature the valve should
close and water only circulate through the radiator system. How fast it
does this will depend on the boiler flow temperature and the tank
thermostat temperature. If for instance the boiler flow and the tank thermostat temperature have both been set to 60C then the hot water may
take a very long time to reach 60C, perhaps never, especially if the
scenario above is true. In my experience the hot water in the tank will
only reach 10C below the boiler flow temperature after an hour or so
when selecting hot water.
Try setting the hot water tank thermostat 10c cooler.
The solution may be to reduce the flow through the hot water path so the
flow resistance through the hot water path equals that of the radiator
path. Balancing radiators via the lockshield valves involves open up
some and CLOSING DOWN further the valve on the radiator where most of
the water is flowing. This doesn't balance the system if most of the
water is flowing through the hot water path.
Perhaps a controller where it can be set to select hot water only before
the heating comes on, or a least for multiple shorter periods where both
are on together.
alan_m <junk@admac.myzen.co.uk> posted:
On 15/12/2024 11:25, Tim+ wrote:
eastender <user150@newsgrouper.org.uk.invalid> wrote:
Several rads just haven't always been getting hot when the timer
switches the central heating and hot water on and it's been driving
me nuts. It's a standard S-plan unvented system boiler arrangement
with two motorised valves, one for each circuit, but with a lot of
rads 17 and an unvented hot water tank. I thought it was air
blocks and/or balancing so have been running around bleeding and
adjusting the lock valves but nothing worked. Anyway today I had the
brainwave of switching the hot water off and leaving the heating on
and lo and behold the rads all came to life. Whats likely to be the
reason? The hot water tank has a thermostat so I would have thought
it should close the valve but maybe it isnt and is causing a
pressure issue of some sort.
Have a look at your pump speed settings (if any). It may be that your pump is failing and doesnt have enough oomph to push water around
your HW tank and CH circuit simultaneously.
Water will always take the path of least resistance which in this case
is likely to be the path through the hot water tank. Pushing up the
pump oomph will not necessarily solve the problem.
What also could be happening is that most of the water is circulating through the hot water tank coils and at speed that return temperature
to the boiler rises close to the flow temperature. The boiler can only modulate down so far and with a high return temperature it has to cut
off or else the flow exceeds the configured flow temperature. To
prevent short cycling the Vaillant EcoTec Plus will now inhibit the
burner firing for perhaps 5 minutes. During this 5 minute period the
flow and return temperature may drop by 10C or more. The lesser amount
of water flowing through the radiators will now be cooler.
Once the hot water has reached the correct temperature the valve should close and water only circulate through the radiator system. How fast
it does this will depend on the boiler flow temperature and the tank thermostat temperature. If for instance the boiler flow and the tank thermostat temperature have both been set to 60C then the hot water may take a very long time to reach 60C, perhaps never, especially if the scenario above is true. In my experience the hot water in the tank
will only reach 10C below the boiler flow temperature after an hour or
so when selecting hot water.
Try setting the hot water tank thermostat 10c cooler.
The solution may be to reduce the flow through the hot water path so
the flow resistance through the hot water path equals that of the
radiator path. Balancing radiators via the lockshield valves involves
open up some and CLOSING DOWN further the valve on the radiator where
most of the water is flowing. This doesn't balance the system if most
of the water is flowing through the hot water path.
Perhaps a controller where it can be set to select hot water only
before the heating comes on, or a least for multiple shorter periods
where both are on together.
Thanks - we need a nw programmer I reckon as the one we have can't cope
with differential CH/hot water settings. I will try turning down the tank stat.
Thanks - we need a nw programmer I reckon as the one we have can't cope with differential CH/hot water settings. I will try turning down the tank stat.
programers know nothing about temperature. That the job of thermostats.
but our programmer can't switch the CH and HW on at different times
charles <charles@candehope.me.uk> posted:
Thanks - we need a nw programmer I reckon as the one we have can't
cope with differential CH/hot water settings. I will try turning down
the tank stat.
programers know nothing about temperature. That the job of thermostats.
Yes, but our programmer can't switch the CH and HW on at different times, only both at the same time unless one is set not to come on at all
although it does have the function of leaving one on and the other off
til the second on time but that can be most of the day.
The thermostat on the tank should though be shutting off the HW but
doesn't always so I will turn down the temp.
programers know nothing about temperature. That the job of thermostats.
programers know nothing about temperature. That the job of thermostats.
John Rumm <see.my.signature@nowhere.null> posted:
On 14/12/2024 18:57, eastender wrote:
Several rads just haven't always been getting hot when the timer
switches the central heating and hot water on and it's been
driving me nuts. It's a standard S-plan unvented system boiler
arrangement with two motorised valves, one for each circuit, but
with a lot of rads – 17 – and an unvented hot water tank. I
thought it was air
So one heating zone and one DHW zone?
blocks and/or balancing so have been running around bleeding and
adjusting the lock valves but nothing worked. Anyway today I had
the brainwave of switching the hot water off and leaving the
heating on and lo and behold the rads all came to life. What’s
likely to be the reason? The hot water tank has a thermostat so
I would have thought it should close the valve but maybe it
isn’t and is causing a pressure issue of some sort.
Chances are the DHW loop has significantly less flow resistance
than the CH circuit, so with both zone valves open, you may get
the bulk of the flow through the DHW circuit. Even if the cylinder
is up to temp, it could still divert flow from the rads.
Much depends on how the system is setup. Ideally you want the DHW
zone to close when the cylinder is at or reaches set point temp.
Since it is probably a very fast recovery cylinder that can absorb
close to the full output of the boiler, operating in DHW priority
mode might make more sense - schedule DHW reheat at times the CH
is not on. You might also find that your boiler is capable of
split temperature operation - i.e. where the boiler knows when it
is heating DHW rather than CH, and can run different flow
temperatures. This allows you to get better condensing efficiency
in the less heating intensive months since the rads can run
cooler, but the DHW is still heated to an adequate temperature to
ensure sanitisation of the water.
You could also take that further and use full weather
compensation:
https://wiki.diyfaq.org.uk/index.php/Weather_compensation
If you really want to run both zones at once on a regular basis,
then adding a manual balancing valve into the DHW primary loop
would help - then you could balance the cylinder with the rads so
that it can't rob them of flow.
Details on S plan configuration here:
https://wiki.diyfaq.org.uk/index.php/
Central_Heating_Controls_and_Zoning#CH_and_DHW_zones:_S-plan
Thanks John - that all makes sense. I think we need a new programmer
- it's this: https://www.plumbworld.co.uk/documents/honeywell-st699- dual-zone-central-heating-timer-user-guide.pdf? srsltid=AfmBOorc0Sj9Fydya4eRct0C8yqpwh0T74h3QV4klWyvrxA844CV-cex
What would be a good alternative that offers more flexibility. I'll
also look at possible split temp operation but presumably that
depends on getting a better programmer at least for months when we
do use the CH.
charles <charles@candehope.me.uk> posted:
Thanks - we need a nw programmer I reckon as the one we have
can't cope with differential CH/hot water settings. I will try
turning down the tank stat.
programers know nothing about temperature. That the job of
thermostats.
Yes, but our programmer can't switch the CH and HW on at different
times, only both at the same time unless one is set not to come on
at all although it does have the function of leaving one on and the
other off til the second on time but that can be most of the day.
charles <charles@candehope.me.uk> posted:most of the day.
Thanks - we need a nw programmer I reckon as the one we have can't cope
with differential CH/hot water settings. I will try turning down the tank >>> stat.
programers know nothing about temperature. That the job of thermostats.
Yes, but our programmer can't switch the CH and HW on at different times, only both at the same time unless one is set not to come on at all although it does have the function of leaving one on and the other off til the second on time but that can be
The thermostat on the tank should though be shutting off the HW but doesn't always so I will turn down the temp.
On 17/12/2024 09:54, eastender wrote:
charles <charles@candehope.me.uk> posted:
Thanks - we need a nw programmer I reckon as the one we have can't cope >>>> with differential CH/hot water settings. I will try turning down the
tank
stat.
programers know nothing about temperature. That the job of thermostats.
Yes, but our programmer can't switch the CH and HW on at different
times, only both at the same time unless one is set not to come on at
all although it does have the function of leaving one on and the other
off til the second on time but that can be most of the day.
The thermostat on the tank should though be shutting off the HW but
doesn't always so I will turn down the temp.
A lot of programmers have a jumper to allow it to either switch hot
water and heating separately or always put hot water on with heating,
worth checking the manual
On 20/12/2024 19:12, Gordy wrote:
On 17/12/2024 09:54, eastender wrote:
charles <charles@candehope.me.uk> posted:
Yes, but our programmer can't switch the CH and HW on at differentThanks - we need a nw programmer I reckon as the one we have can't
cope
with differential CH/hot water settings. I will try turning down
the tank
stat.
programers know nothing about temperature. That the job of thermostats. >>>
times, only both at the same time unless one is set not to come on at
all although it does have the function of leaving one on and the
other off til the second on time but that can be most of the day.
The thermostat on the tank should though be shutting off the HW but
doesn't always so I will turn down the temp.
A lot of programmers have a jumper to allow it to either switch hot
water and heating separately or always put hot water on with heating,
worth checking the manual
The OPs programmer can do that - but it is just down to how you wire the relay outputs.
On 21/12/2024 00:06, John Rumm wrote:
On 20/12/2024 19:12, Gordy wrote:It says the programmer can't switch the CH and HW at different times,
On 17/12/2024 09:54, eastender wrote:
charles <charles@candehope.me.uk> posted:
Thanks - we need a nw programmer I reckon as the one we have can't >>>>>> cope
with differential CH/hot water settings. I will try turning down
the tank
stat.
programers know nothing about temperature. That the job of
thermostats.
Yes, but our programmer can't switch the CH and HW on at different
times, only both at the same time unless one is set not to come on
at all although it does have the function of leaving one on and the
other off til the second on time but that can be most of the day.
The thermostat on the tank should though be shutting off the HW but
doesn't always so I will turn down the temp.
A lot of programmers have a jumper to allow it to either switch hot
water and heating separately or always put hot water on with heating,
worth checking the manual
The OPs programmer can do that - but it is just down to how you wire
the relay outputs.
this isn't down to the wiring, it is when the programmer fires the
relays, that was my point, you can often set a jumper such that if you
only ask for heating it may or may not also fire the hot water relay.
No it doesn't - I posted a link to one of the manuals earlier, however
ere is another with more detail of operation:
https://www.free-instruction-manuals.com/pdf/p4734641.pdf
On 21/12/2024 10:13, Gordy wrote:
On 21/12/2024 00:06, John Rumm wrote:
On 20/12/2024 19:12, Gordy wrote:It says the programmer can't switch the CH and HW at different times,
On 17/12/2024 09:54, eastender wrote:
charles <charles@candehope.me.uk> posted:
Thanks - we need a nw programmer I reckon as the one we have
can't cope
with differential CH/hot water settings. I will try turning down >>>>>>> the tank
stat.
programers know nothing about temperature. That the job of
thermostats.
Yes, but our programmer can't switch the CH and HW on at different
times, only both at the same time unless one is set not to come on
at all although it does have the function of leaving one on and the
other off til the second on time but that can be most of the day.
The thermostat on the tank should though be shutting off the HW but
doesn't always so I will turn down the temp.
A lot of programmers have a jumper to allow it to either switch hot
water and heating separately or always put hot water on with
heating, worth checking the manual
The OPs programmer can do that - but it is just down to how you wire
the relay outputs.
No it doesn't - I posted a link to one of the manuals earlier, however
ere is another with more detail of operation:
https://www.free-instruction-manuals.com/pdf/p4734641.pdf
Some selected highlights for you :
"ST699 INCORPORATES THE FOLLOWING FEATURES:
24-hour programme
Independent Heating and Hot Water control"
"The unit has two ON/OFF programme times per day to control your Heating
and Hot Water system. To help you set your personal programme quickly, a built-in programme has been incorporated with commonly used programme
times. This programme is selected automatically when the unit is first connected to the mains power or when the RESET button is pressed.
Each programme time can be set between 3.00am and 2.50am (on the next
day) to allow you to programme past midnight, if required."
And in particular:
"IMPORTANT NOTICE
When using ST699/ST799 on gravity hot water/pumped heating systems, a
HEATING & HOT WATER sticker (supplied) should be placed over the
existing HEATING caption (as illustrated below)."
In other words, combined heating and DHW only applies on systems with
gravity hot water, not fully pumped systems.
this isn't down to the wiring, it is when the programmer fires the
relays, that was my point, you can often set a jumper such that if you
only ask for heating it may or may not also fire the hot water relay.
I think you have a misunderstanding of how and why the interaction
between heating and DHW can come about on some partially pumped systems.
If used on a fully pumped system, then there is independent control of
the primary flow from the boiler through the rads and the cylinder. You
can have one or the other or possibly both. This flow is controlled by
one or more zone valves.
With some partially pumped systems that only have gravity circulation
through the cylinder, initially there were no valves at all. Just a pump
for circulating water through the rads. So when the boiler fires, the cylinder is heated - all the time, whether it needs to be or not. If you
also want heating, the the boiler fires *and* the pump is also run.
In that situation you have two calls for heat - one to fire the boiler
and one to run the pump. However they are not fully independent since whichever causes the boiler to light will get a DHW reheat.
When you use a two channel programmer like the ST699 on these systems,
even though its CH and DHW outputs are fully independent and separately timed, the system itself can't actually heat the rads in isolation. That
is not down to a limitation of the programmer (but they do supply a
sticker to apply to the face of it to make this more clear!)
On 21/12/2024 12:36, John Rumm wrote:
No it doesn't - I posted a link to one of the manuals earlier, however
ere is another with more detail of operation:
https://www.free-instruction-manuals.com/pdf/p4734641.pdf
Isn't that the programmer the OP is thinking of getting rather than the
one he has.
Thanks John - that all makes sense. I think we need a new programmer - it's this:
https://www.plumbworld.co.uk/documents/honeywell-st699-dual-zone-central-heating-timer-user-guide.pdf?srsltid=AfmBOorc0Sj9Fydya4eRct0C8yqpwh0T74h3QV4klWyvrxA844CV-cex
On 21/12/2024 12:36, John Rumm wrote:
On 21/12/2024 10:13, Gordy wrote:I think we are at cross purposes, my system at home it is a Y plan, but doesn't use the CH off terminal so when just HW is selected the 3 port
On 21/12/2024 00:06, John Rumm wrote:
On 20/12/2024 19:12, Gordy wrote:It says the programmer can't switch the CH and HW at different times,
On 17/12/2024 09:54, eastender wrote:
charles <charles@candehope.me.uk> posted:
Thanks - we need a nw programmer I reckon as the one we have
can't cope
with differential CH/hot water settings. I will try turning down >>>>>>>> the tank
stat.
programers know nothing about temperature. That the job of
thermostats.
Yes, but our programmer can't switch the CH and HW on at different >>>>>> times, only both at the same time unless one is set not to come on >>>>>> at all although it does have the function of leaving one on and
the other off til the second on time but that can be most of the day. >>>>>>
The thermostat on the tank should though be shutting off the HW
but doesn't always so I will turn down the temp.
A lot of programmers have a jumper to allow it to either switch hot
water and heating separately or always put hot water on with
heating, worth checking the manual
The OPs programmer can do that - but it is just down to how you wire
the relay outputs.
No it doesn't - I posted a link to one of the manuals earlier, however
ere is another with more detail of operation:
https://www.free-instruction-manuals.com/pdf/p4734641.pdf
Some selected highlights for you :
"ST699 INCORPORATES THE FOLLOWING FEATURES:
24-hour programme
Independent Heating and Hot Water control"
"The unit has two ON/OFF programme times per day to control your
Heating and Hot Water system. To help you set your personal programme
quickly, a built-in programme has been incorporated with commonly used
programme times. This programme is selected automatically when the
unit is first connected to the mains power or when the RESET button is
pressed.
Each programme time can be set between 3.00am and 2.50am (on the next
day) to allow you to programme past midnight, if required."
And in particular:
"IMPORTANT NOTICE
When using ST699/ST799 on gravity hot water/pumped heating systems, a
HEATING & HOT WATER sticker (supplied) should be placed over the
existing HEATING caption (as illustrated below)."
In other words, combined heating and DHW only applies on systems with
gravity hot water, not fully pumped systems.
this isn't down to the wiring, it is when the programmer fires the
relays, that was my point, you can often set a jumper such that if
you only ask for heating it may or may not also fire the hot water
relay.
I think you have a misunderstanding of how and why the interaction
between heating and DHW can come about on some partially pumped systems.
If used on a fully pumped system, then there is independent control of
the primary flow from the boiler through the rads and the cylinder.
You can have one or the other or possibly both. This flow is
controlled by one or more zone valves.
With some partially pumped systems that only have gravity circulation
through the cylinder, initially there were no valves at all. Just a
pump for circulating water through the rads. So when the boiler fires,
the cylinder is heated - all the time, whether it needs to be or not.
If you also want heating, the the boiler fires *and* the pump is also
run.
In that situation you have two calls for heat - one to fire the boiler
and one to run the pump. However they are not fully independent since
whichever causes the boiler to light will get a DHW reheat.
When you use a two channel programmer like the ST699 on these systems,
even though its CH and DHW outputs are fully independent and
separately timed, the system itself can't actually heat the rads in
isolation. That is not down to a limitation of the programmer (but
they do supply a sticker to apply to the face of it to make this more
clear!)
valve is driven all the way over to divert all flow to the HW tank coil
When CH is selected the HW output is also energised to 'liven up' the
valve and the CH on contact will drive the valve to center position.
When the thermostat on the tank is satisfied the valve will divert fully
to CH.
On all the timers I have fit to this system there is a jumper to enable either completely separate outputs for CH or HW or it can be set to fire
the HW relay when only CH is selected.
In any case it looks like the ST699 doesn't have this.
No offense intended, it's good to talk!
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