why might hot water in one bathroom to be tepid ?

[starfry]

I just signed up to see if anyone can offer any suggstions with a problem I'm experiencing with my hot water. I've been a reader for a while but never had a reason to post anything until now.

A few days ago the water in one of my bathrooms stopped getting hot. Having investigated a bit, it's only in this room - everywhere else is fine. There is plenty of hot water. Furthermore, if I run both basins or one basin and the shower then the water comes out hot. If I turn off one thing, the remaining one goes tepid.

I isolated the cold supply to test and confirmed that the unwanted cold water is coming through the hot supply pipe.

It's an unvented system with a "Gledhill stainless lite" indirect 300L cylinder with a pumped secondary return.

Can anyone suggest what this might be? I'll probably need to get someone in but I would like to at least have an idea of what the problem is.

Thanks.

 

[TeaTime]

What else draws hot water in that room?
Are you just experiencing it in the basin?
What type of taps is installed?

 

[starfry]

The room has a bath, separate shower and two basins. Nothing else draws water in that room.

The basin taps are mixers, bath has a thermostatic mixer and the shower also has a thermostatic mixer.

Both basins get hot if both are on. If one turned off then the other goes tepid. Likewise shower is tepid until flow is drawn from either basin. Similarly for bath.

It was all working fine until last week.

 

[TeaTime]

Is the pressures relatively balanced for cold / hot water or is the cold water supply pressure significant in comparison?

 

[starfry]

I think they're pretty balanced. There's little difference between the flow rate with just cold and just hot.

I did test to see what happened if I cut off the cold supply to the basin (by closing in-line isolating valve). With no cold supply at the tap the problem was the same, so I don't think it's due to the cold supply in the bathroom.

 

[picasso]

sticking nrv on the secondary return would cause this (amongst other things).

 

[starfry]

Thanks, why doesn't it affect the other bathrooms/kitchen, etc...?

 

[picasso]

It was just a thought its more likely one of the nrv in the shower has stuck and causing the cold ater to pass into the hot system.

 

[starfry]

The secondary has a Grundfos 97549426 pump on it. Can't see anything separate that looks like nrv - would this be integrated into the pump?

The shower controls are a IS A3969NU Trevi TT shower valve. Again not sure, but would any nrv there be part of the valve?

getting concerned about having to break decorated surfaces ...

 

[picasso]

The secondary pump should have a nrv between the pump and the cylinder, your trevi valve has access to the nrvs from the front so no need to break anything.

 

[starfry]

Well, it turns out that the problem was caused by the stat on the bath mixer. After turning that through its full range and leaving it on the default setting, everything is now working as it should.

The mixer is IS A4616 Attitude Thermostatic Two Hole Bath Shower Mixer with Shower Set.