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Default CH Pump Overrun

My Ideal Logic boiler goes into 'pump overrun' on occasion while the
thermostat is calling for heat. It goes into overrun, then purge, when the
temperature's reached as part of the normal cycle, but I've only just noticed
this while it's actually heating.

Seems odd to me - if the boiler is trying to 'spread heat' why does it get so
hot in the first place?

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On 17/01/2021 09:47, RJH wrote:
My Ideal Logic boiler goes into 'pump overrun' on occasion while the
thermostat is calling for heat. It goes into overrun, then purge, when the
temperature's reached as part of the normal cycle, but I've only just noticed
this while it's actually heating.

Seems odd to me - if the boiler is trying to 'spread heat' why does it get so
hot in the first place?


I would expect the pump to run continuously whilst the room thermostat
is calling for heat.

I would expect the pump to be running (overrun) when the call for heat
has been met and the boiler has just stopped firing. If the pump stopped
immediately the static water in the heat exchanger would get too hot
because it would be still heated due to boiler components in the heating
path (heat exchanger etc.) still being hot. A bit like turning off an
oven and the food still cooking until the oven cools down after a period
of time.

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On 17/01/2021 09:59, alan_m wrote:
On 17/01/2021 09:47, RJH wrote:
My Ideal Logic boiler goes into 'pump overrun' on occasion while the
thermostat is calling for heat. It goes into overrun, then purge, when
the
temperature's reached as part of the normal cycle, but I've only just
noticed
this while it's actually heating.

Seems odd to me - if the boiler is trying to 'spread heat' why does it
get so
hot in the first place?


I would expect the pump to run continuously whilst the room thermostat
is calling for heat.

I would expect the pump to be running (overrun) when the call for heat
has been met and the boiler has just stopped firing. If the pump stopped
immediately the static water in the heat exchanger would get too hot
because it would be still heated due to boiler components in the heating
path (heat exchanger etc.) still being hot.Â* A bit like turning off an
oven and the food still cooking until the oven cools down after a period
of time.

The pump is controlled by main thermostat. The boiler firing is *also*
controlled by water circulation temperature.

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On 17/01/2021 10:10, The Natural Philosopher wrote:
On 17/01/2021 09:59, alan_m wrote:
On 17/01/2021 09:47, RJH wrote:
My Ideal Logic boiler goes into 'pump overrun' on occasion while the
thermostat is calling for heat. It goes into overrun, then purge,
when the
temperature's reached as part of the normal cycle, but I've only just
noticed
this while it's actually heating.

Seems odd to me - if the boiler is trying to 'spread heat' why does
it get so
hot in the first place?


I would expect the pump to run continuously whilst the room thermostat
is calling for heat.

I would expect the pump to be running (overrun) when the call for heat
has been met and the boiler has just stopped firing. If the pump
stopped immediately the static water in the heat exchanger would get
too hot because it would be still heated due to boiler components in
the heating path (heat exchanger etc.) still being hot.Â* A bit like
turning off an oven and the food still cooking until the oven cools
down after a period of time.

The pump is controlled by main thermostat.


Some/many boilers control the pump, and have a built in overrun timer to
run the pump longer than the main thermostat demands.

The boiler firing is *also*
controlled by water circulation temperature.


Yes


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On 17 Jan 2021 at 10:10:49 GMT, "The Natural Philosopher"
wrote:

On 17/01/2021 09:59, alan_m wrote:
On 17/01/2021 09:47, RJH wrote:
My Ideal Logic boiler goes into 'pump overrun' on occasion while the
thermostat is calling for heat. It goes into overrun, then purge, when
the
temperature's reached as part of the normal cycle, but I've only just
noticed
this while it's actually heating.

Seems odd to me - if the boiler is trying to 'spread heat' why does it
get so
hot in the first place?


I would expect the pump to run continuously whilst the room thermostat
is calling for heat.

I would expect the pump to be running (overrun) when the call for heat
has been met and the boiler has just stopped firing. If the pump stopped
immediately the static water in the heat exchanger would get too hot
because it would be still heated due to boiler components in the heating
path (heat exchanger etc.) still being hot.Â* A bit like turning off an
oven and the food still cooking until the oven cools down after a period
of time.

The pump is controlled by main thermostat. The boiler firing is *also*
controlled by water circulation temperature.


OK, thanks both, I think I get it! So it's not a problem then.

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The Natural Philosopher formulated on Sunday :
The pump is controlled by main thermostat.


Not in modern boilers. In modern boilers the pump is controlled by the
boiler and the boilers determines when the pump needs to run. Basically
as soon as flame is detected, through to burn turned off and remaining
heat removed from the boilers heat exchanger. Very sensible too, why
waste the heat? My boiler also exercises the pump and the fan, if they
haven't had need to run for a while.
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on 17/01/2021, The Natural Philosopher supposed :
The boiler firing is *also* controlled by water circulation temperature.


Modern boilers do what is called modulate - the Kw output can be varied
over a range of output, to suit the heat for HW or CH requirement.
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RJH has brought this to us :
OK, thanks both, I think I get it! So it's not a problem then.


It might be, if the boiler manufacturer specifies that the pump has to
be directly controlled by the boiler.
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On 17/01/2021 19:47, Harry Bloomfield wrote:
The Natural Philosopher formulated on Sunday :
The pump is controlled by main thermostat.


Not in modern boilers. In modern boilers the pump is controlled by the
boiler and the boilers determines when the pump needs to run.


In my ancient boiler the pump is wired to and controlled by the boiler.

Assuming that the timers are set to on... if there a call for water
heating or central heating the boiler will turn the pump on. The pump
will remain on continuously until one of the thermostats indicates the
temperature has been reached and then the overrun kicks in leaving the
pump running until the boiler water outlet has cooled down. During the
time that the pump is being effectively controlled by the thermostat(s)
the burner will cycle on and off. More modern boilers may modulate the
burner flame in order to reduce cycling.

On my boiler there is a temperature sensor attached to the boiler outlet
pipe. This heats a bi-metal strip which in turn switches an over-run
mirco-switch. The micro-switch supplies one source on mains to the pump
when the boiler outlet pipe is still hot.

There is also a safety electrical over temperature cut off switch bolted
to the boiler outlet pipe.

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In article ,
Harry Bloomfield wrote:
The Natural Philosopher formulated on Sunday :
The pump is controlled by main thermostat.


Not in modern boilers. In modern boilers the pump is controlled by the
boiler and the boilers determines when the pump needs to run. Basically
as soon as flame is detected, through to burn turned off and remaining
heat removed from the boilers heat exchanger. Very sensible too, why
waste the heat? My boiler also exercises the pump and the fan, if they
haven't had need to run for a while.


you say modern boilers. Mine, which I installed in 1989, has this. very
necessary if you have zone valves.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle


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In article ,
Harry Bloomfield wrote:
on 17/01/2021, The Natural Philosopher supposed :
The boiler firing is *also* controlled by water circulation temperature.


Modern boilers do what is called modulate - the Kw output can be varied
over a range of output, to suit the heat for HW or CH requirement.


I installed a modulating boiler in our last house in the early 1970s.

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"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
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On 17/01/2021 09:47, RJH wrote:
My Ideal Logic boiler goes into 'pump overrun' on occasion while the
thermostat is calling for heat. It goes into overrun, then purge, when the
temperature's reached as part of the normal cycle, but I've only just noticed
this while it's actually heating.

Seems odd to me - if the boiler is trying to 'spread heat' why does it get so
hot in the first place?


I don't quite understand what you are saying. How are you detecting that
the pump is over-running? Which thermostat is calling for heat - the
boiler stat or the room stat? Is the boiler controlling the pump?

By definition, pump over-run only occurs when the boiler is *not*
firing, but has has some residual heat which needs to be dissipated to
prevent it overheating. [The metal heat exchanger will be a lot hotter
than the water in it, and will continue to heat the water in it if there
is no flow - possibly to the point where the over-heat cutout trips].
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Roger
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On 17/01/2021 19:47, Harry Bloomfield wrote:

Very sensible too, why
waste the heat?


On my boiler when the overrun became much too short in duration and cut
off too early the water in the copper heat exchanger started boiling and
the whole boiler started banging - loudly. The idea of the overrun is
not to prevent wasting heat but to continue to distribute any heat via
the flowing water to prevent localised short term overheating in the boiler.

On my boiler the over-run switch is electro mechanical and the "pip" on
a micro-switch had worn. It was easily fixed with an adjustment screw
being wound down quarter of a turn. The PITA was that a liquid screw
lock had been used previously which required some heat from a large
soldering iron to free the adjustment again.


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On 17 Jan 2021 at 20:40:34 GMT, "Roger Mills" wrote:

On 17/01/2021 09:47, RJH wrote:
My Ideal Logic boiler goes into 'pump overrun' on occasion while the
thermostat is calling for heat. It goes into overrun, then purge, when the
temperature's reached as part of the normal cycle, but I've only just
noticed
this while it's actually heating.

Seems odd to me - if the boiler is trying to 'spread heat' why does it get
so
hot in the first place?


I don't quite understand what you are saying. How are you detecting that
the pump is over-running?


Firstly by sound - I noticed it had stopped 'firing' while the room stat was
calling for heat. Confirmed by the on-boiler display.

Which thermostat is calling for heat - the
boiler stat or the room stat? Is the boiler controlling the pump?


The room stat controls the boiler. The boiler controls the pump. I don't know
the boiler's relationship with the pump, though.


By definition, pump over-run only occurs when the boiler is *not*
firing, but has has some residual heat which needs to be dissipated to
prevent it overheating. [The metal heat exchanger will be a lot hotter
than the water in it, and will continue to heat the water in it if there
is no flow - possibly to the point where the over-heat cutout trips].


Yes, that's what I'm asking. It would make more sense to me the throttle back
the gas in the first place, rather than let it get hot to the point that it
needs to cool down by pumping the hot water away.

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Cheers, Rob


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On 17/01/2021 20:40, Roger Mills wrote:
On 17/01/2021 09:47, RJH wrote:
My Ideal Logic boiler goes into 'pump overrun' on occasion while the
thermostat is calling for heat. It goes into overrun, then purge, when
the
temperature's reached as part of the normal cycle, but I've only just
noticed
this while it's actually heating.

Seems odd to me - if the boiler is trying to 'spread heat' why does it
get so
hot in the first place?


I don't quite understand what you are saying. How are you detecting that
the pump is over-running? Which thermostat is calling for heat - the
boiler stat or the room stat? Is the boiler controlling the pump?

By definition, pump over-run only occurs when the boiler is *not*
firing, but has has some residual heat which needs to be dissipated to
prevent it overheating. [The metal heat exchanger will be a lot hotter
than the water in it, and will continue to heat the water in it if there
is no flow - possibly to the point where the over-heat cutout trips].


Boiler pumps run continuously as long as there is a call for heat. The
burner will cut out when the *circulation* temperature reaches the
desired setting.


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people by telling poor people that "other" rich people are the reason
they are poor.

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In article , The Natural Philosopher
wrote:
On 17/01/2021 20:40, Roger Mills wrote:
On 17/01/2021 09:47, RJH wrote:
My Ideal Logic boiler goes into 'pump overrun' on occasion while the
thermostat is calling for heat. It goes into overrun, then purge, when
the temperature's reached as part of the normal cycle, but I've only
just noticed this while it's actually heating.

Seems odd to me - if the boiler is trying to 'spread heat' why does it
get so hot in the first place?


I don't quite understand what you are saying. How are you detecting
that the pump is over-running? Which thermostat is calling for heat -
the boiler stat or the room stat? Is the boiler controlling the pump?

By definition, pump over-run only occurs when the boiler is *not*
firing, but has has some residual heat which needs to be dissipated to
prevent it overheating. [The metal heat exchanger will be a lot hotter
than the water in it, and will continue to heat the water in it if
there is no flow - possibly to the point where the over-heat cutout
trips].


Boiler pumps run continuously as long as there is a call for heat. The
burner will cut out when the *circulation* temperature reaches the
desired setting.


you're missing over run. Particularly when the circulation is controlled
by zone valves, the heast in the boiler needs somewhere to go, so a valve
stays open and the pump continues to run for a time controlled by the
boiler.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
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On 18/01/2021 05:49, RJH wrote:
On 17 Jan 2021 at 20:40:34 GMT, "Roger Mills" wrote:



Yes, that's what I'm asking. It would make more sense to me the throttle back
the gas in the first place, rather than let it get hot to the point that it
needs to cool down by pumping the hot water away.


Irrespective of how intelligent your thermostat it is basically an
on/off switch. The boiler has no prior knowledge that the thermostat is
going to tell it to turn off and without this prior information cannot
throttle back in the way you suggest.

Whilst there is a call for heat the boiler is trying to almost instantly
raise the temperature of a very fast flow of water in a VERY short run
of pipe by 10C. A boiler may have some intelligence to increase the
burner when the incoming water is at 20C, with an expected output of 60C
which it cannot achieve instantly, and modulate the burner down when the
incoming water is 50C, again with an expected output of 60C. To raise
the water by 10C almost instantly the heat exchanger is at a much higher
temperature even when the burner is turned down to low.

The boiler may be operating at the low burner mode for, say, half an
hour before the room heats up enough for the room thermostat to cut in.
The boiler, without warning, is told to shut down. The boiler throttles
back the gas by the largest amount it can by turning the burners off.
Even with the burner turned off the heat exchanger still is hot enough
to raise a fast flowing steam of water by 10C+ and if the flow of water
is stopped by very much more than 10C.

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alan_m explained on 18/01/2021 :
The boiler may be operating at the low burner mode for, say, half an hour
before the room heats up enough for the room thermostat to cut in. The
boiler, without warning, is told to shut down. The boiler throttles back the
gas by the largest amount it can by turning the burners off. Even with the
burner turned off the heat exchanger still is hot enough to raise a fast
flowing steam of water by 10C+ and if the flow of water is stopped by very
much more than 10C.


The only thing the boiler can use, to know to throttle back, is an
increasing flow (or return) from the boiler temperature - where the
room stat is simple on/off. Throttling has to work almost blindly.

My Vaillant, with its fancy control system goes one step further. It
knows the actual room temperature (or hot cylinder temperature) and
knows the desired temperature. From the two values, it knows how much
heat it needs to still produce, to avoid producing too much heat, so it
can throttle itself precisely to hit the requirement.
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In article ,
Harry Bloomfield wrote:
alan_m explained on 18/01/2021 :
The boiler may be operating at the low burner mode for, say, half an hour
before the room heats up enough for the room thermostat to cut in. The
boiler, without warning, is told to shut down. The boiler throttles back the
gas by the largest amount it can by turning the burners off. Even with the
burner turned off the heat exchanger still is hot enough to raise a fast
flowing steam of water by 10C+ and if the flow of water is stopped by very
much more than 10C.


The only thing the boiler can use, to know to throttle back, is an
increasing flow (or return) from the boiler temperature - where the
room stat is simple on/off. Throttling has to work almost blindly.


My Vaillant, with its fancy control system goes one step further. It
knows the actual room temperature (or hot cylinder temperature) and
knows the desired temperature. From the two values, it knows how much
heat it needs to still produce, to avoid producing too much heat, so it
can throttle itself precisely to hit the requirement.


That what my 1972 vintage boiler did. Wish I could remember the make.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
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charles brought next idea :
That what my 1972 vintage boiler did. Wish I could remember the make.


I have come across commercial systems which did similar, but I didn't
know home heating systems had the technology until fairly recently.


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On 18 Jan 2021 at 20:39:11 GMT, "Harry Bloomfield, Esq."
wrote:

alan_m explained on 18/01/2021 :
The boiler may be operating at the low burner mode for, say, half an hour
before the room heats up enough for the room thermostat to cut in. The
boiler, without warning, is told to shut down. The boiler throttles back
the
gas by the largest amount it can by turning the burners off. Even with the
burner turned off the heat exchanger still is hot enough to raise a fast
flowing steam of water by 10C+ and if the flow of water is stopped by very
much more than 10C.


The only thing the boiler can use, to know to throttle back, is an
increasing flow (or return) from the boiler temperature - where the
room stat is simple on/off. Throttling has to work almost blindly.

My Vaillant, with its fancy control system goes one step further. It
knows the actual room temperature (or hot cylinder temperature) and
knows the desired temperature. From the two values, it knows how much
heat it needs to still produce, to avoid producing too much heat, so it
can throttle itself precisely to hit the requirement.


Yes, that's what I'd have thought my Ideal Logic might have offered. But
seemingly not.

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In article ,
Harry Bloomfield wrote:
The Natural Philosopher formulated on Sunday :
The pump is controlled by main thermostat.


Not in modern boilers. In modern boilers the pump is controlled by the
boiler and the boilers determines when the pump needs to run. Basically
as soon as flame is detected, through to burn turned off and remaining
heat removed from the boilers heat exchanger. Very sensible too, why
waste the heat? My boiler also exercises the pump and the fan, if they
haven't had need to run for a while.


Fairly certain mine also modulates the pump speed. Oh - it doesn't have a
thermostat as such. A room temperature sensor. All or nothing is a very
old way of controlling heat.

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Dave Plowman London SW
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On 19/01/2021 10:47, Dave Plowman (News) wrote:


Fairly certain mine also modulates the pump speed. Oh - it doesn't have a
thermostat as such. A room temperature sensor. All or nothing is a very
old way of controlling heat.


Modern pumps can be set for fixed speeds or autonomous proportional control.

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In article ,
alan_m wrote:
On 19/01/2021 10:47, Dave Plowman (News) wrote:



Fairly certain mine also modulates the pump speed. Oh - it doesn't
have a thermostat as such. A room temperature sensor. All or nothing
is a very old way of controlling heat.


Modern pumps can be set for fixed speeds or autonomous proportional
control.


Mine is part of a system boiler. Controlled by the boiler processor.

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Dave Plowman London SW
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