Shower allowing hot water into cold feed

[bgs264]

Background:
I have an outhouse with its own cold feed (with own stopcock).

The hot feed into the outhouse is provided via a combi boiler in the main house - and therefore is controlled by the stopcock on the cold feed to the house.

Therefore, to totally isolate both hot and cold water in the outhouse, I need to turn off both stopcocks. One in the outhouse, one in the main house.

Problem:
If I isolate the cold feed in the outhouse, then I start to get hot water in my cold taps including the cold supply to the washing machine and also the outdoor taps.

Hypothesis:
There is a bar/mixer shower in the outhouse connected to the outhouse's cold feed and the hot being driven from the main house. In this situation when I turn off the outhouse cold feed and get hot water out the cold taps, the shower itself is getting very hot to touch even though it's not being used. I think that the shower is allowing hot water to pass through into the cold water pipes of the outhouse.

What's the fix?
I was considering buying a new bar/mixer shower. I found one on Amazon - the "Hapilife Square Thermostatic Bar Shower Mixer" which shows it has both hot and cold check valves. I'm hoping these check valves within the shower itself will stop the ability for hot water to pass through the shower into the cold feed, when the cold feed is isolated.

Does this seem like a sensible fix? Or is there something cheaper I could do, I was thinking perhaps I could add some check valves myself between the inlets and the shower but the only ones I can find seem to be smaller and intended to fit onto a shower hose to prevent dirty water syphoning back into the system if the shower hose/head is submerged.

Thanks.

 

[PETE 123]

non return valves in shower mixer letting by had the same thing.

 

[SJB060685]

I suspect the mixer shower internally has failed, both the shower and NRV would have to have failed if there were NRV's. I take it this is a recent problem and the boiler ignites when you have this flow?

 

[bgs264]

Yep you're right. It's a recent problem and the boiler ignites. It's how we found out about it - wondering why the boiler was igniting when we had nothing on except the washing machine and felt the inlet hose of the washer, which surely enough was warm.

Hopefully, a new shower will fix it then. Seems like a sensible fix?

 

[SJB060685]

Yep you're right. It's a recent problem and the boiler ignites. It's how we found out about it - wondering why the boiler was igniting when we had nothing on except the washing machine and felt the inlet hose of the washer, which surely enough was warm.

Hopefully, a new shower will fix it then. Seems like a sensible fix?

The simple fix is NRV's on hot and cold to shower, although this only masks the problem, it still doesn't prevent the crossflow.

 

[bgs264]

Is the crossflow a symptom of a faulty shower, is fitting a new shower the "correct" fix to this? Thanks for your help.

 

[SJB060685]

Is the crossflow a symptom of a faulty shower, is fitting a new shower the "correct" fix to this? Thanks for your help.

Showers are not my speciality, im an oil engineer by trade. You might get away with replacing internal parts to stop this problem. @ShaunCorbs can you clarify? See what Shaun has to say mate and if you decide to replace the mixer shower then install NRV's on the hold and cold to the shower as well. That way you will prevent this problem in the future if the shower was to become faulty again.

 

[bgs264]

Showers are not my speciality, im an oil engineer by trade. You might get away with replacing internal parts to stop this problem. @ShaunCorbs can you clarify? See what Shaun has to say mate and if you decide to replace the mixer shower then install NRV's on the hold and cold to the shower as well. That way you will prevent this problem in the future if the shower was to become faulty again.

Thanks for your help!

 

[ShaunCorbs]

I would test your theory first whip the shower off and cap the supplies temp then try your test again and see if you get warm mixing if you don’t then there’s your problem and either a new shower or to fit some external check valves to the shower

 

[Ben-gee]

Remove the bar shower valve and see if it has built in nrv, most have them behind the captive nuts that screw onto your pipework.

They can get stuck open if the spring goes off to one side, or the plastic components can break up. It is usually quite easy to get them out and they can be replaced - but if it were me I would get a new valve (Mira, hansgrohe, etc) not some cheap rubbish for £40 - you only need to spend £100-£120 for something decent.

 

[bgs264]

Thanks for the help everyone. I swapped the shower over and the problem is resolved