Hansgrohe thermostatic shower not working

[Jackson1980]

I have a hot and cold pump for my shower. The shower is a Hansgrohe thermostatic mixer valve. When I turn on the shower the pump isn't triggered to turn on and the water dribbles from the shower head. However, If I turn the temp. dial on the shower mixer to cold, and the shower power to max, the pump will turn on. As I turn the temp up the shower pump shuts off. If I turn the temp to cold it will turn on again, but if I turn the temp valve very slowly the shower stays on.

So far I have: cleaned the filters on the pump, checked the cold water flow rate before the pump and the hot water flow rate before the pump and both are well within spec. I have removed the shower head and tested the system without it fitted to the pipe, and the system does the same as described above. I have also let the shower flow on full hot and full cold for 10 mins each to clear air from the pipes.

Without the shower head on the pipe, the flow rate fluctuates from normal flow rate, to nothing and then back to normal flow rate as I turn the temp. dial from cold to hot.

I have changed the thermostatic cartridge in the shower mixer valve.

Anyone know what is going on here? What do I do next?

 

[ShaunCorbs]

Anything changed before the problem started ?

 

[Ben-gee]

Hot inlet filter to the shower is blocked?

 

[Jackson1980]

Anything changed before the problem started ?

Hi, no. When first installed it was fine for 12 months then this problem started!!

 

[Jackson1980]

Hot inlet filter to the shower is blocked?

Hi, unfortunately not. I cleared the filters on the shower and the pump!

 

[ShaunCorbs]

Was both installed or just the pump 12 months ?

 

[Jackson1980]

Was both installed or just the pump 12 months ?

Both - it was a new en-suite fit out

 

[ShaunCorbs]

Is it a handheld unit or just eg rain head ?

 

[Jackson1980]

Hand held spray head only - no rain head

 

[ShaunCorbs]

Does it work if you lower the head to the base ?