thermostatic valve shower OK bath lukewarm

[chocadooby]

I have a thermostatic valve and diverter supplying my shower and bath through a bath filler. The temperature of the shower is fine, but the temperature of the bath water starts at the right temperature for about 2-3 seconds, then goes lukewarm.

The thermostatic valve is supplied by mains cold and the combi boiler (Bosch Worcester Greenstar 28) for hot. It has never worked and I have had it a year - we just avoided having baths, however a baby is on the way so we need it working.

Can anybody please help?

Many thanks

Chocadooby

 

[Bahco]

Try only opening the bath tap a little and see if the water gets hot.

 

[chocadooby]

That seems to work, as the water heats up somewhat. Why is this happening?

 

[Bahco]

Thats how combis work.

They only heat the water as you need it .

The less water going through the boiler, the hotter it gets.

 

[chocadooby]

So if the shower water is always at a good temperature, then does that mean that the shower head is restricting the flow, thereby giving a decent temperature?