Shower going cold

[YorkieJohn]

Our shower runs from the combi boiler, and when showering runs hot then can run cold then go back hot again. This happens when only the shower is run no taps are on or the washer. Any ideas what it could be ? The plumbing firm we have had in have tried everything but not solved it. The boiler is a gloworm fairly old but the plumbers think that after tests it seems ok. It does not happen on any of the taps just the shower.

[Catso]

If you have a thermostatic shower control, it could be faulty or having something stuck in it.

But if you've had professional plumbers look, I don't know what else to suggest. New boiler? Ouch!

[naz_nomad]

Do your radiators get hot when ONLY the hot water is on?

[WendyS]

Is somebody flushing a toilet somewhere else in the house while somebody is having a shower, or running a tap down in the kitchen?
Sometimes this can result in sudden extreme temperature changes in the water coming through the shower.

[wilsarnie]

Happened to our Vokera boiler twice.

First the thermostatic (?) valve had gone.

Second was the fan inside that was dirty and wasn't spinning around all the time and that's why it went cold.

Our plumber was rubbish and couldn't fix the problem. We went directly to Vokera and they sent someone out for a flat fee in the next two days and fixed it no problem.

I guess you can't always expect plumbers to know every thing about every boiler.