Thermostatic mixing valve issue

[JohnD]

Have you got a hot water cylinder? What colour?

 

[Gossamer]

Where is the mixing valve? Can you post a sketch?

The pipes are like spaghetti! Having looked at the layout it seems ok. It’s getting hot and cold feeds for sure so no incorrect pipe park that I can see.

Do you have an airlock in the hot supply? Or even a foreign object that has been sucked down from the cwsc.

Something has changed in the pressure differential. Either hot has reduced or cold has increased or valve to equalise has failed.

The cold pressure seems higher than usual.
It might not be relevant but the boiler suddenly need topping up like there’s a leak. Could it be a prv on the main feed has popped and has found a weak point? It’s a residential block so a few flats are served by it.

Have you got a hot water cylinder? What colour?

Thanks etc are in the loft and I’ve not looked tbh.

 

[JohnD]

I’ve not looked tbh.

please do.

 

[Gossamer]

please do.

Am I looking for the overall colour of the cylinder? The ones I’ve seen are usually white.

 

[JohnD]

the colour of other cylinders is irrelevant.

What matters is if you have one, and, if so, what colour it is.

 

[dilalio]

Or. Just send a photo.
I have enough cryptic clues from "paying" customers FFS.

 

[Johntheo5]

The pipes are like spaghetti! Having looked at the layout it seems ok. It’s getting hot and cold feeds for sure so no incorrect pipe park that I can see.

The cold pressure seems higher than usual.
It might not be relevant but the boiler suddenly need topping up like there’s a leak. Could it be a prv on the main feed has popped and has found a weak point? It’s a residential block so a few flats are served by it.

Thanks etc are in the loft and I’ve not looked tbh.

Boiler top up has no relevance.

What make is the new (and old, if available) TMV??, from what I've now read, the "average" max pressure ratio to allow mixing would appear to be 5:1, if you have a gravity head of 0.5bar, then the max mains pressure cannot exceed 2.5bar, a dedicated PRV should have no problem in getting down to 1.5bar or even less.

 

[Gossamer]

UPDATE: after reducing the cold main and getting the TMV working I fitted a PRV which seems to have solved the problem.
I could leave the cold at full pressure and reduce the cold feed into the TMV so it worked properly. Everything works as it should.
The cold was overpowering the hot feed into the TMV (maybe 3 bar v <1 bar?). Quite why this suddenly become an issue for the TMV requiring a PRV is unknown. Thames Water did some work in the area recently but it seems only this flat was affected.
Thanks all.

 

[Johntheo5]

What pressure have you set the PRV to?

 

[Gossamer]

What pressure have you set the PRV to?

I don't know.....
It came with a blanking plug (?) installed and a gauge. Couldn't find the gauge after install, so adjusted it until everything was working. Then found the gauge and CBA to isolate and an swap it with the blanking plug...... I assume it will be fine?!