Thermostatic shower mixer too cold in winter

[zeroid]

We have a combi boiler (Glow Worm 24CX) and a thermostatic shower mixer tap. The mixer tap looks like its a few years old but still functions as it should (in the summer).

In the winter however its only possible to get the shower hot enough by turning the temp round to maximum (the red override button no longer functions by the way) and turning the tap right down so there is barely enough pressure for the shower to operate.

Now I know there will be slightly less hot water flow/output from the boiler in the winter due to lower incoming water temperature, but the valve seems to be letting cold through too - surely the valve should only be letting through the hot feed if set to the hottest setting.

Does anyone know if this should be the case (and a new mixer would improve the situation), or is it actually that all these valves will let through some cold and hot in all situations. If the latter then would I be better using a non-thermostatic mixer so that I can force the system to give me just the hot water feed so I know I'm getting the best flow that the boiler can give?

Thanks...

 

[muggles]

It could be that your thermostatic mixer simply needs a new cartridge, or it could have an over-temperature safety on it. Failing that it may well be that the boiler simply isn't keeping up in the winter. What make/model of mixer is it? I wouldn't fit a non-thermostatic mixer to a combi

 

[zeroid]

Its a "Tivoli II" (see pic below). How can I tell if the cartridge can be changed in this?

I think the boiler is up to the job - I can get hot water from a tap at a reasonable flow (in winter).

Here is a pic of the mixer:

A few other discussions I read were recommending Mira CombiForce 415 as ideal for combi, yet it's not themostatic?

 

[flameport]

Its a "Tivoli II" (see pic below). How can I tell if the cartridge can be changed in this?

It can be changed, or at least removed for cleaning/descaling and reassembled, the maximum temperature can also be adjusted.

That shower is actually a Tivoli Solo, the instructions are here:
http://www.bristan.com/WebRoot/BristanDB/Shops/Bristan/Products/INSTRUC. PDF-1032384-D2.PDF

If it needs a new cartridge, it is probably better to just replace the whole thing.

 

[seco services]

Checked the filters in the rear of the mixer ?

 

[zeroid]

Thanks for the instructions, I'll see if I can strip it down and take a look at some point.