Fluctuating shower temp - thermostatic mixer . . .

27 Dec 2006
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United Kingdom
Hi all, have a thermostatic mixer shower, fed from a 2 yr old worsceter bosch greenstar combi boiler - hot water in kitchen is a constant temp but shower has started fluctuating during showering.

I'm assuming this is a lime scale issue? The mixer is of the 'bar' type and I see there is a small screw underneath the mixer on the heat adjustment end of the 'bar'. I am assuming this is a retaining screw and the working parts can be removed for cleaning? Anyone know if this is true?

Also, would i have to shut down water supply to mixer?

thanks for any help!

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is the boiler cutting in/out when the temp on the shower alters ?
maybe the dhw diaphragm faulty.
the shower can be the first appliance to pic this fault up.

try running the shower with a hot tap on.
Hi, thanks for swift response. I don't think it is, however will test with tap running as you suggest.

is my lime scale theory unlikely ? also, is it likely a diaphram on a boiler wear out after only 2 years? (I live alone so it hasn't had really heavy use)

yes the diaphragm could fail in that amount of time, but it is more likely the cartridge in the bar mixer is shot.
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thanks - have run the shower with another hot tap on and it is still fluctuating - assume this points towards the bar mixer cartridge then?

can I remove it to inspect? shot as is totally SHOT, or can it be cleaned ?

yes remove the cartridge and give a good clean to remove the limescale.
may even need a new cartridge.
thanks - so to remove the cartridge do i jsut remove the small screw on underside of bar and extract cartridge? does the water supply to mixer bar need to be shut off ?

depends what bar mixer it is make/model.

yes you have to isolate the hot/cold supply or you'll get soaked.

useally the temp dial needs to be remove to gain access to the cartridge.

I agree with everyones response. Must emphasis the importance of checking if ur boiler is burning continuously when shower is running or if its fluctuating on/off. If it is, will be a boiler issue and not the shower. Has happened to me on the job so thought would be worth letting you know as some replacement cartridges are expensive, especially if you don't need it.

Run your shower as before then go stand in front of your boiler. U should be able to tell if its fired up and staying on or if its stop/starting if it is then the boiler is the prob.....

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