Hot water stops when a cold water tap is open (flow rate is good!) - new Combi boiler

[ARM76]

Hi

I moved from a conventional boiler to a combi - Worcester Greenstar 30i (two bed flat, with one bathroom). Everything works fine, heating, hot water etc. The only problem is when I try to run hot and cold water together the boiler switches off and no hot water comes through (the flow of water from the hot tap doesn't change). To be more precise I can turn the hot water tap on in the bath and hot water runs, nice and toasty. The moment I turn the cold water on, the boiler turns off. The thermostatic shower does something similar but I don't even get any hot water, the boiler initially starts up the moment you turn the shower on but then instantly stops. In the bathroom sink the cold and hot taps are separate taps. If I run the hot water in the sink it runs hot, when run a cold water tap anywhere in the flat the boiler switches off (again the flow rate barely drops). I initially thought the flow was dropping and the boiler was turning off but the flow from the boiler seems fine....

Any ideas what the problem is and are British Gas liable to rectify the situation as they installed the boiler?

TIA
Andrew

 

[Newboy]

Sounds like either low flow or low pressure or both.

Worth checking that your mains stopcock is fully open.

Did BG check static & dynamic pressure and flow rates prior to installing a combi?

 

[Agile]

If you want accurate advice then give us proper information please.

Who had the boiler installed?

When was it installed?

When did you come to it?

Has it always done this since installation?

I suspect there is some form of crossover.

But will need a good plumber to identify the defect in the pipework.

Have you fitted any washing machine or dish washer?

Tony

 

[ARM76]

British gas installed the boiler two days ago, problem happened since then. I have a dish washer and washing machine, I live alone. When I was testing the water I made sure nothing else was running at the time.

Not sure BG tested the flow rate, I went with their recomendation (what I know about plumbing you could write on the back of a pastage stamp). Mains is fully open and each flat has a separate supply. Flow rate and pressure appears good, certainly its higher than other flats I've lived in with Combi's.

Thanks
A.

 

[Newboy]

Sorry - I misread your post. The hot water continues to run but runs cold?

Whatever the issue, get BG back.

 

[ARM76]

Yup, thats correct, water flowing ok but the boiler turns off, I've stood in the kitchen and watched it. When I turn the cold tap off boiler comes back. I'll see what BG have to say. Thanks for your help.

A.

 

[dilalio]

BG are big and ugly enough to have the after sales support to put this right for you. You may have to stamp your feet a bit but it needs to be them you call. If the process becomes drawn out you can inform them that you would like a second opinion (boiler manufacturer would be a good source) and that you will be billing BG for it.

 

[Agile]

Please make sure that you find out exactly what the problem is and tell us here.

Because there is no obvious common explanation.

Were all the machines there before the boiler?

Tony

 

[Agile]

With the boiler cold, run a hot tap and feel the pipes under the boiler and tell us clearly which pipe gets hot please!

 

[dilalio]

Without further hands on investigation,
the most plausible explanation would be that water finds the path of least resistance and is taking a course through piperuns to your cold outlets, rather than the extra effort required to go through your boiler, to be heated and then delivered at the hot outlets.