Thermostatic Shower Problem

[iddon]

only getting luke-warm water even when set to max from Bristan Sonique thermo valve. It's a single lever operated valve. Cartridge only recently installed in last 4 weeks replacing one that would not turn. Runs off a Worcester Bosch Greenstar 37 cdi and woked fine up until 24 hours ago. Bristan rep suggests checking cold water pressure by running shower at full temp, then running cold water from basin to check in any fluctuation and then flushing WC.
Any thoughts? Just seems a little odd that the temperature has failed so quickly.

 

[HITGAS]

check the non return valves to see that they are not stuck.

 

[iddon]

Re. Non return valve - where should I be looking? Is it going to be along either the HW or CW feeds from the Combi? (excuse me for being a bit thick on this)

 

[iddon]

Forget to mention that the HW inlet into the Shower mixer is hot and having further increased the water temperature at source on the combi. Have also ran a pressure test by turn basin cold water tap on for a minute which had no effect on temperature and then flushed WC which had a minor impact for about a minute before the shower reverts back to cold/luke-warm.

 

[HITGAS]

Non return valves are usually on the inlet to the shower.

 

[iddon]

Just spoken with Bristan Technical again, aaaaaaaaaarrrrrrgggghhhh.
Having been asked to check the water pressure by running the cold water in the sink and then giving the loo a flush theyh now tell me this has nothing to do with the problem and that it's likely that by removing the cartridge, cleaning it and then a smear of silicon should fix as they are known for sticking. Will clean it this evening and see what results.