Is it possible for a failed thermostatic bath mixer tap to cause crossover problems

[angefoh]

I have a central heating with storage tank system. I woke this morning to what sounded like running water, although no taps were turned on.
I went to my boiler room in the basement and the pressure valve was reading 10 psi and water was running out via the pressure release valve outlet. I turned off the hot water supply to the upstairs bathroom and the running water sound stopped. I then went up stairs and ran the mixer tap for the sink and although the hot water supply was turned off I was getting water from the hot side but this turned out to be cold water.
I have a failed thermostatic valve (3 months) on my bath mixer tap, and I am wondering if this has suddenly caused a crossover problem.
Please anyone know if this is the case or has other suggestions as to what may have caused the problem. Thanks in anticipation.
Andrew.

 

[Riley]

10psi is about 0.5 bar most pressure relief valves on boilers don’t kick in until three bar. What do you have? Boiler? Cylinder? Pics would be useful of the pipework involved. I’m not sure what you think has crossed over

 

[angefoh]

10psi is about 0.5 bar most pressure relief valves on boilers don’t kick in until three bar. What do you have? Boiler? Cylinder? Pics would be useful of the pipework involved. I’m not sure what you think has crossed over

OK The issue I have is I am recovering from a broken ankle so the fewer stairs I do the better. Anyway the system is a Valiant boiler with a storage tank for the hot water. It has been fine for many months. I have recently installed an up stairs bathroom and tee-ed off the hot water for this with a shut of valve. the sound of running water stopped when I closed this valve and the downstairs hot water supply is fine.
I have read that failed mixer valves can cause cross over issues and this I think is whats happened. And I meant to say the pressure meter was 10 bar not 10 psi.

 

[Riley]

Very confusing query, for a start the pressure gauge on your boiler will not be showing psi Do you perhaps have an unvented cylinder ?? Crossover could potentially cause the cold from the hot side but is extremely unlikely to be opening a prv

 

[rpm]

10 bar !!!? with prv open?

 

[Riley]

10 bar would be a hell of a pressure. Hence why I queried psi but it would only do it if it were an unvented as all other prvs are on heating side

 

[angefoh]

10 bar would be a hell of a pressure. Hence why I queried psi but it would only do it if it were an unvented as all other prvs are on heating side

OK I will go and check again. As I said I am a little restricted movement wise. I'll get some pictures of the prv and meter.
thanks for your help so far.

 

[Riley]

No worries. Happy to help but doingbit blind is sometimes difficult

 

[angefoh]

OK I am a complete fool. The PRV's are on the central heating side of the boiler and as the picture shows the meter is between 2 prv's. So some how the hot water supply to the upstairs has caused this issue and I am not sure how to reduce this pressure safely. Pressure to the radiators is a nominal 1 bar and seems to be working fine.
How do I reduce the pressure safely.

 

[Riley]

Right following that valve leads to your hot water cylinder does it? You really need a G3 registered engineer out to look at it as you are not qualified to work on that particular feature. What you have there is a pressure reducing valve. Not quite sure of the tie in with your thermostatic valve failure but it could just be an unhappy coincidence.