Thermostatic shower and bath filler not hot

Hi everyone.
I have a bath with overhead shower the bath is Bristan quest or something like, the overhead rainfall shower is a good brand from stax. Sp I think. Both cost over £150 so not cheap. But neither has water coming out hot enough just a little better than lukewarm unless I restrict the flow then I get a hot trickle.

The bath is obviously more of a problem. The basin is non thermostat so lovely and hot as is kitchen and ensuite shower.
Now the pipes right up to bath filler are 22mm and the same pipes feed the basin which is lovely and hot.
Obviously if I control the flow the water will get hot but it takes ages to fill the bath and can’t really enjoy a rainfall shower when it’s slowed to a trickle.
To mimic reduced flow I’ve restricted isolator valves but again I don’t want it to be a trickle.
I’ve taken off the quarter turn fitting and turned valve on hot and refitted cap so the cartridge is turned to max. Nothing.
I’ve obviously played with button for the anti scold safety again nothing as I’ve taken the turning cap off and moved it maximum anyway.
So could anybody suggest what else I could do. Thanks.

Are they high or low pressure valves?
What hot water system do you have?

dilalio said:

Are they high or low pressure valves?
What hot water system do you have?

Click to expand...

Sorry it’s a combi boiler. Main 30kw. The boiler is fine though as it’s really hot everywhere else.

Remove thernostatic cartridge and test water coming straight out of valve.
If you get good supply then the cartridge needs cleaning/replacing.
You might also be getting crossflow.

Ok so I did remove cartridge on both the shower and bath filler and saw that they were retracting as I turned so appear to be working ok. What is crossflow?

Solved this by restricting the cold water flow from the isolator