Hansgrohe thermostatic shower not working

[John.g]

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?

If you have a negative head pump then a pressure switch starts the pump and (I think there are two) the flow switches stop it so the hot side flow switch may be defective, you can test them with a magnet.
If positive head then the flow switches start/stop the pump but same problems might apply.

 

[Ben-gee]

How hot is your hot water?

I have seem a ST pump where excessive hot water temperature had caused the problem you are having. The flow switch had a “ball in a cage” the hot had distorted the cage so that the ball was not free to rise and fall as it should.

It only takes the hot water to be too hot for a short while to do this.

 

[Timmy D]

How hot is your hot water?

I have seem a ST pump where excessive hot water temperature had caused the problem you are having. The flow switch had a “ball in a cage” the hot had distorted the cage so that the ball was not free to rise and fall as it should.

It only takes the hot water to be too hot for a short while to do this.

I agree with this. I’ve also come across this issue. Got new flow switches and it was resolved.

Isolate the pump both electricity and wet. Remove out let hoses (be ready for a bit of water). Remove flow switches and check inside, you’ll likely find the hot one deformed.

 

[Jackson1980]

I agree with this. I’ve also come across this issue. Got new flow switches and it was resolved.

Isolate the pump both electricity and wet. Remove out let hoses (be ready for a bit of water). Remove flow switches and check inside, you’ll likely find the hot one deformed.

The hot water temp is not excessive by any means. Where do I get a service kit for the Salamander pump? Where-ever the service kit appears online it says it is discontinued?

Thanks

 

[steadyon]

Are there any non-return valves in the shower itself or in the relevant hot and cold pipework? These can become faulty and stick (open (usually) or closed). If there are any, try cleaning / descaling them.

 

[Jackson1980]

No, not as far as I'm aware.