Boiler Issue

[BigRooster]

My Bosch worchester greenstar boiler has just been serviced by british gas and given a full bill of health .
Now the problem is my thermostatic shower goes hot and cold but yet all my taps can run all day with out this happening .
I've been told the shower unit may be faulty so I've replaced it but it still does the same hot then after a few mins cold for about 10 secs .
So what could it be ??

[Zacs-Master]

Which part of the shower did you replace?

[BigRooster]

Thermostatic shower unit I was told that the cartridge may be faulty or bloked

[bookbinder]

Try entering 'thermostatic mixing valve problems' in your search engine. You might get some help there.

[Old_Geezer]

It cycles hot & hot ? Sounds like it is too sensitive. Needs a little hysteresis. Unsure what you can do but get the engineer in again.

Actually my shower has been playing up over the last few months. I have a cold tank in the loft which must keep constant pressure I assume, but still the temperature starts too hot but changes as I shower. Have to keep adjusting. Darn things.

[BigRooster]

Water comes straight from my combi boiler just frustrated that changer thermostatic unit hasn't worked

[The Builder]

If you're happy that this never happens at the taps, then it still points to a shower fault.

What's the make and model number of the shower?

[rccatnap]

About once a year, because we have hard water, I de-scale the mixing cartridge using ordinary kettle de-scaler.
The calcium builds up in the mixing barrel and restricts the movement, so prevents one getting the right temperature.
As mentioned before, Google the your model and search for the assembly/maintenance manual. You'll also need to have some silicone grease for re-assembly. Good luck.