Combi hot/cold crossover in shower mixer

[drpepe]

Hi, a heating engineer came to fix my combi, but ended up concluding that there’s a hot/cold water crossover caused by the thermostatic valve in my shower (he checked the tsps and mixers on all the other basins ).

However he ‘only does boilers’ so he didn’t want to touch the shower

Can I just replace the valve on the right hand side to fix this? Is it as simple as turning off the water unscrewing and replacing ?

Many thanks

 

[picasso]

The nrvs are in the wall mount supply to the shower , you would need to take the shower off the wall and clean or replace .

 

[drpepe]

Is it part of the mixer or could it be anywhere on the pipes leading in?

 

[picasso]

Its part of the mixer, if you undo the large nuts holding the shower to the wall the nrvs are in the "legs".

 

[drpepe]

Thanks that's really helpful.

Just switch water off at the stop tap?

 

[picasso]

Might be a good idea unless you fancy doing it in scuba gear.

 

[Johntheo5]

I would test for boiler PHEX blockage for fouling first, turn the DHW temperature to max on the boiler, open any one hot water tap fully, if it remains hot, open any remaining hot taps fully, if the water then runs cold, quite possibly the PHEX. Set the the shower to its hottest setting and open the flow control to give a fairly low flow or until hot, then open it up to give full flow, does it then run cold shortly afterwards?.

 

[drpepe]

Thanks. Should be covered by the investigation the engineer did? He took apart the exchanger as he'd assumed it was kaput. He took the filter out and cleaned that too.

 

[Johntheo5]

He probably did but the HEX could still be scaled up, the filter, if choked, only slows the water flow so the DHW temp should still be OK except its ridiculously as low as ~ 2/2.5 LPM in which case the flow switch will prevent the boiler c/o to DHW and firing up.
If the PHEX is scaled then the primary flow temperature will just keep increasing to its burner trip limit of around 85C. You can monitor this on some boilers.
The above tests will, IMO, give a good indication of this.

That filter may be on the primary flow to the PHEX but still worth carrying out tests IMO.

 

[drpepe]

He did say the water temp coming out of the boiler was good

 

[Johntheo5]

So then only problem is with the shower at all flow rates?, you have no hot water at any flow rate.

 

[drpepe]

Sorry. The issue is tepid/variable water in all the basins and the shower. I got the engineer out as I thought it was a boiler issue.
After trying a few things the engineer came to conclusion that there's a crossover in the shower.