Water from cold tap is delivered hot

[nrplum32]

Hi all,

Wonder if you could help to diagnose my issue with a Worcester Bosch 28cdi in a ground floor flat which started delivering hot water when the cold water tap in the kitchen is opened - it's not just few seconds of hot water, the boiler fires and delivers hot water for the duration while the cold water tap is on, and turns off when the tap is closed. The bathroom cold water taps unaffected and runs cold. Hot water tap works as expected everywhere.

I think there was some work done on the communal water tank on the roof on the same time as this started, though I am unsure if either the kitchen or bathroom is indeed connected to it and if this really had any effect though it seemed to happen at the same time. I read on the forum about something similar, that the boiler can fire for a short time once the tap is either opened or closed, caused by a 'dead leg' in the pipework, but in my case it fires for the duration the tap is on and behaves like a hot water tap.

Does anyone know if it's the work to the water storage tank that caused this, or something else e.g. a problem with the boiler?

Thanks,
Nigel

 

[KingDoey]

You shouldn't be connected in any way to the storage cisterns in the loft if you have a combi.

Sounds very strange. So your cold tap on the kitchen sink is suddenly behaving as your hot tap would? Has anyone altered any pipe work under your sink or in your flat at all recently?

 

[Chuck]

Does anyone know if it's the work to the water storage tank that caused this, or something else e.g. a problem with the boiler?

You have an unusual problem.

I suggest you start by asking the company responsible for the recent water tank work whether they think it's possible that their work was responsible. Use email so if they deny responsibility you have it in writing. Next get whoever services your boiler to come and check the boiler. If it's not a boiler problem you want a plumber, possibly with a thermal imaging camera, to figure out what's happening and fix it.

 

[Gasmk1]

Is the water warm from this tap if so it could be a faulty tap allowing the hot to mix with the cold, I would say it's a faulty mixer tap only way to be sure is to feel pipes going to the tap when you turn on cold if the hot pipe gets hot then there is the proof that the tap is faulty and needs replacing

 

[nrplum32]

Hi KingDoey, Chuck and Gasmk1,

Thanks for your suggestions.

I have a query out with the management company about what work they did (thanks Chuck), meanwhile I managed to get it functioning ok - sort of.

I played with the valves under the sink - one tap I am not sure about, the next affects the flow to both hot/cold kitchen taps, but the third seemed to control the amount of flow from the cold and hot tap before the boiler triggers. I found that fully open both hot and cold taps would not trigger the boiler even when opened to the max, and fully closed both hot and cold taps would trigger the boiler after with very little flow (and water would be very hot). In between there was a spot that took hours to find where the cold tap could be opened a normal amount and remain cold and where the hot tap would trigger after being opened just a little, while being hot enough. I didn't manage to find a perfect spot and if the cold water it opened to the max it triggers.

Thinking about what KingDoey said, it's likely I am not connected to the communal tank with my combi, so what may have happened is as part of the work on it, the company may have turned off the supply to the entire block (including my flat's supply) and turned it back, but at a slightly different flow/pressure than before, causing my strange 3rd tap to need adjustment.

Would be great to hear if this is standard plumbing, or if it sounds like something is still wrong!

Thanks again.

Regards,
Nigel

 

[Chuck]

Would be great to hear if this is standard plumbing, or if it sounds like something is still wrong!

No, that's not how standard plumbing should work. Stop-cocks with a traditional 'crutch' handle should normally simply be opened fully and then closed about a quarter turn. If there is some reason to limit the flow then there'll be a second lock-shield valve, which requires a tool to adjust, in series with it.

Anyway, I think you need to get a reputable plumber, who'll need to be Gas Safe Registered, to investigate your boiler and how it's been installed. We could play twenty questions to try and figure out exactly what the problem is, but I think that the answer is still going to be 'call a plumber'.

 

[galaxy_plumbing]

I second to a faulty mixer tap.