Thermostatic shower valve 'clunk' question

[Paul Edwards]

I have a dull thermostatic shower valve question.
My daughter is complaining that when she turns her shower off to shampoo her hair (It's a small shower), and then back on again to continue showering, it’s gone cold, regardless of the fact that there's still residual hot water in the pipe.
Trying to replicate that myself, I’ve noticed it doesn’t stay cold forever, the mixer makes a single dull clunk noise, and then it returns to hot again.
Can something get stuck in these things? And can it be fixed/freed-up? It hasn't always done this. It seems to have developed recently, having been fitted for about 4 years.
We live in a hard water area, so wondering if that's anything to do with it?
FYI, it’s one of these - https://www.victorianplumbing.co.uk/trafalgar-traditional-twin-concealed-thermostatic-shower-valve

 

[Madrab]

Unfortunately, I would have to point towards it being a thermo valve issue. Trafalgar are a 'generic' import sold by VPlumbing and as such I'm afraid to say they may not be the best of quality. That coupled with being in a hard water area will compound the issue.

Being a concealed valve it won't be the easiest to service either. Parts availability will be another concern.

The clunk could be the thermostatic vial/piston jamming then freeing up with the 'clunk' but without stripping it, it would be hard to be sure.

 

[Paul Edwards]

Thanks loads for the reply Rob.
I can get to the valve, just by slicing through the silicon holding the chrome face/coverplate to the wall and removing it, so accessibility shouldn't be that much of an issue. Could it be a case of stripping, cleaning/descaling, and refitting the piston? Or are these valves non-servicable?
Obv. If the worst comes to the worst, I'll replace the entire thing, but ideally this is fixable.

 

[Madrab]

Could it be a case of stripping, cleaning/descaling, and refitting the piston

Depends on how it's constructed. Some have wax pistons that control the H/C flow, others have a complete thermostatic module where the whole thing is replaced.

Certainly nothing lost by stripping it down and having a look and giving it a service.

 

[Paul Edwards]

Certainly nothing lost by stripping it down and having a look and giving it a service.

Thanks again Rob. I will certainly give it a go.