combi boiler firing up when cold tap turned off

[velasquez]

Hi, first time on here - I would greatly appreciate any advice on the following problem: My Worcester 24i RSF combi boiler has begun to fire up when any cold tap is turned off after running, however briefly (also includes wc cistern fill). Although the flame cuts out quickly, obviously the fan then runs on for several minutes. This has started to happen after some minor changes to the kitchen plumbing - the sink being moved across the room. It appears that the boiler is somehow sensing a pressure change causing it to fire up to meet a demand for hot water. I spoke to a tech adviser at Worcester who was sure it was a plumbing issue and not a boiler one; I also spoke to a plumber, who was sure it was a boiler issue. The house plumbing is very simple at the moment: The main comes in (1/2" lead, soon to be replaced) and from the stopcock a 15mm copper pipe supplies everything. First tee branch goes upstairs to bathroom then another tee, one side to kitchen sink, one side to boiler, both within a few feet. The mains pressure is very good but I have tried partially closing the stopcock to varying degrees - this worked at first (briefly) but does not now. I have also tried partially closing the valve at the cw inlet to the boiler but no joy. (it's supposed to be able to take 10 bar pressure anyway!) The hot water is also 15mm and uncomplicated and there are definitely no crossovers or connections between hot/cold/ch or anything substantially different to what was there before.

I think that's all I can say - any help would be great!

 

[45yearsagasman]

Its possible that your water system, having been altered now has a dead leg causing your problem.(a section of pipe that has not been bled and contains air) Your installer should be able to rectify this. Failing that the fitting of a small expansion vessel on the cold supply may be a solution.

 

[velasquez]

Thanks for that 45yearsagasman, it was indeed a deadleg. I went back over everything and cross-searched the forum finding some other references to similar problems. Pinged up floorboards until I found hidden under the bathroom floor at the back of the bath was a capped off pipe which must have fed the bath from the old cylinder. I bled it and that seems to have done the trick! I will remove it soon but at least that's stopped the boiler problem.

 

[45yearsagasman]

Well done and thanks for the thanks

 

[Whitespirit66]

//www.diynot.com/forums/viewtopic.php?p=1968025#1968025

 

[annesd]

Hello

I have developed exactly the same problem with our boiler. The only difference is that yesterday we had some new ceramic disc cartridges fitted in the bath taps upstairs to deal with a dripping tap. The plumber turned off the water at the mains (obviously) replaced the cartridges and turned the mains water back on. He did not touch the boiler nor had any reason to. Now, when a cold water tap is turned off or the toilet stops flushing the fan on the boiler turns on. It's as though the boiler is confused and thinks the hot water has been running instead of the cold. The heating part of the system works fine.

Is this a boiler problem ? If so I have insurance with British Gas so I would call them out. The thing is, as I say all the plumber did was deal with a dripping tap - there was no issues with the boiler before

 

[jeff the gasman]

You too have air in the pipework.
Cure as above..
Jeff

 

[Bunnyman]

Same as above , open all hot an cold taps to chk no air, also any old washing machine taps? New machines are cold fill only so u may have an old hot one not connected behind machine, open it until water comes out. If not then u have a deadleg somewhere as per original poster

 

[Servotech]

Hello

I have developed exactly the same problem with our boiler. The only difference is that yesterday we had some new ceramic disc cartridges fitted in the bath taps upstairs to deal with a dripping tap. The plumber turned off the water at the mains (obviously) replaced the cartridges and turned the mains water back on. He did not touch the boiler nor had any reason to. Now, when a cold water tap is turned off or the toilet stops flushing the fan on the boiler turns on. It's as though the boiler is confused and thinks the hot water has been running instead of the cold. The heating part of the system works fine.

Is this a boiler problem ? If so I have insurance with British Gas so I would call them out. The thing is, as I say all the plumber did was deal with a dripping tap - there was no issues with the boiler before

Highly likely that the plumber who turned off the mains turned the stop tap back on full when he turned your water supply back on - try turning it down (anti-clockwise) first.

servotech,

 

[kbdiy]

try turning it down (anti-clockwise) first.

servotech,

errr clockwise surely?

 

[Liamb023]

This sounds like your cold water mains pressure is too high, try turning your stop tap down slightly or fitting a pressure reducing valve to the cold feed to the boiler.
If it is too high what happens when you turn off the cold tap the water the back pressure down the pipe causes the water to trigger the flow switch in the boiler, so the boiler thinks youve opened the hot tap