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Hot water 'boiling over' into header tank
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- Lemon Quarter
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Hot water 'boiling over' into header tank
We are intending to replace the ancient (1980s I suspect) boiler and HWC in the new place, but due to various unexpected expenditure this might have to wait until after winter.
When the hot water is on, the boiler cuts in and out and there is loads of bubbling and gurgling from the pipework. I fitted an auto air vent to the top of the CH pipework, but not the HW pipework.
What is really odd is that when the HW is switched off and the pump stops, there is a 2-3 second gush of water from the pipe exiting the top of the HW cylinder into the header tank. It doesn't do it when running as far as I've noticed, only when it stops.
Any clues?
Thanks
Paul
When the hot water is on, the boiler cuts in and out and there is loads of bubbling and gurgling from the pipework. I fitted an auto air vent to the top of the CH pipework, but not the HW pipework.
What is really odd is that when the HW is switched off and the pump stops, there is a 2-3 second gush of water from the pipe exiting the top of the HW cylinder into the header tank. It doesn't do it when running as far as I've noticed, only when it stops.
Any clues?
Thanks
Paul
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- Lemon Half
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Re: Hot water 'boiling over' into header tank
Partially blocked cold fill tee, probably.
Tiny leaks on the system mean it is constantly being refilled and the new water gives up it's calcium at the point it joins the heating system and gets heated. Once there is a build-up, the venturi effect or similar causes low (or high) pressure at the tee to shift the relative levels in the tank and the vent pipe when the pump is running. When the pump stops, the levels equalise but the open vent overshoots.
Tiny leaks on the system mean it is constantly being refilled and the new water gives up it's calcium at the point it joins the heating system and gets heated. Once there is a build-up, the venturi effect or similar causes low (or high) pressure at the tee to shift the relative levels in the tank and the vent pipe when the pump is running. When the pump stops, the levels equalise but the open vent overshoots.
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- Lemon Quarter
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Re: Hot water 'boiling over' into header tank
can be caused by pump located in wrong part of the system.
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- Lemon Half
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Re: Hot water 'boiling over' into header tank
We had this once, and it is due to the pump being fitted into the flow pipe rather than the return pipe.
It can be cured by reducing the pump pressure or by putting it in the correct line.
TJH
It can be cured by reducing the pump pressure or by putting it in the correct line.
TJH
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- Lemon Half
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Re: Hot water 'boiling over' into header tank
tjh290633 wrote:We had this once, and it is due to the pump being fitted into the flow pipe rather than the return pipe.
It can be cured by reducing the pump pressure or by putting it in the correct line.
TJH
Not necessarily. I've seen this happening in dozens if not hundreds of installations where the pump is already in the 'correct' pipe.
Up until about 1980 the correct location for the pump was considered to be in the return pipe to the boiler. Then thinking changed (I never understood why) to it needing to be in the flow pipe.
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- Lemon Quarter
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Re: Hot water 'boiling over' into header tank
We had this happen a couple of years ago with a Potterton boiler. Turned out to be a boiler thermostat that needed replaceing.
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- Lemon Quarter
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Re: Hot water 'boiling over' into header tank
Mike4 wrote:Up until about 1980 the correct location for the pump was considered to be in the return pipe to the boiler. Then thinking changed (I never understood why) to it needing to be in the flow pipe.
I was told (so it might be wrong) that pumps were fitted to the cooler return pipe so that they lasted longer. A downside is that air can be drawn in through micro-leaks due to part of the system being under negative relative pressure. Modern winding wire insulation can withstand much higher temperatures than the old stuff so there is no real disadvantage to fitting a new pump to the flow.
Julian F. G. W.
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- Lemon Quarter
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Re: Hot water 'boiling over' into header tank
DrFfybes wrote:We are intending to replace the ancient (1980s I suspect) boiler and HWC in the new place
As an aside, if the boiler is old enough to be venting through a chimney, remember that new ones cannot (unless the chimney can be opened for inspection along its run - which it won't).
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- Lemon Quarter
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Re: Hot water 'boiling over' into header tank
stewamax wrote:DrFfybes wrote:We are intending to replace the ancient (1980s I suspect) boiler and HWC in the new place
As an aside, if the boiler is old enough to be venting through a chimney, remember that new ones cannot (unless the chimney can be opened for inspection along its run - which it won't).
The boiler is in a kitchen undercounter cupboard so vents onto the patio. The new boiler will have to move.
Thanks
Paul
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