Donate to Remove ads

Got a credit card? use our Credit Card & Finance Calculators

Thanks to johnstevens77,Bhoddhisatva,scotia,Anonymous,Cornytiv34, for Donating to support the site

Hot water 'boiling over' into header tank

Does what it says on the tin
DrFfybes
Lemon Quarter
Posts: 3732
Joined: November 6th, 2016, 10:25 pm
Has thanked: 1171 times
Been thanked: 1964 times

Hot water 'boiling over' into header tank

#339378

Postby DrFfybes » September 10th, 2020, 9:22 am

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

Mike4
Lemon Half
Posts: 7086
Joined: November 24th, 2016, 3:29 am
Has thanked: 1637 times
Been thanked: 3794 times

Re: Hot water 'boiling over' into header tank

#339424

Postby Mike4 » September 10th, 2020, 11:46 am

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.

jackdaww
Lemon Quarter
Posts: 2081
Joined: November 4th, 2016, 11:53 am
Has thanked: 3203 times
Been thanked: 417 times

Re: Hot water 'boiling over' into header tank

#339613

Postby jackdaww » September 11th, 2020, 9:18 am

can be caused by pump located in wrong part of the system.

:idea:

tjh290633
Lemon Half
Posts: 8209
Joined: November 4th, 2016, 11:20 am
Has thanked: 913 times
Been thanked: 4097 times

Re: Hot water 'boiling over' into header tank

#339623

Postby tjh290633 » September 11th, 2020, 9:45 am

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

Mike4
Lemon Half
Posts: 7086
Joined: November 24th, 2016, 3:29 am
Has thanked: 1637 times
Been thanked: 3794 times

Re: Hot water 'boiling over' into header tank

#339636

Postby Mike4 » September 11th, 2020, 10:34 am

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.

richlist
Lemon Quarter
Posts: 1589
Joined: November 4th, 2016, 3:54 pm
Has thanked: 33 times
Been thanked: 477 times

Re: Hot water 'boiling over' into header tank

#339643

Postby richlist » September 11th, 2020, 10:56 am

We had this happen a couple of years ago with a Potterton boiler. Turned out to be a boiler thermostat that needed replaceing.

jfgw
Lemon Quarter
Posts: 2540
Joined: November 4th, 2016, 3:36 pm
Has thanked: 1097 times
Been thanked: 1147 times

Re: Hot water 'boiling over' into header tank

#339741

Postby jfgw » September 11th, 2020, 6:06 pm

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.

stewamax
Lemon Quarter
Posts: 2417
Joined: November 7th, 2016, 2:40 pm
Has thanked: 83 times
Been thanked: 782 times

Re: Hot water 'boiling over' into header tank

#339885

Postby stewamax » September 12th, 2020, 1:32 pm

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).

DrFfybes
Lemon Quarter
Posts: 3732
Joined: November 6th, 2016, 10:25 pm
Has thanked: 1171 times
Been thanked: 1964 times

Re: Hot water 'boiling over' into header tank

#340135

Postby DrFfybes » September 14th, 2020, 9:08 am

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


Return to “Building and DIY”

Who is online

Users browsing this forum: No registered users and 9 guests