Shower pump problem

[murphs14]

Good afternoon, I hope someone out there can help me. I have a Watermill shower pump. When I turn on the water flow at the shower mixer on cold the pump starts and we have flow. When I turn the temperature control towards the hot, the pump stops. Any ideas anyone please?

 

[Gasguru]

Flow switch on the pump hot side failed or sticking or poor hot flowrate.

If you turn off the pump do you get sufficient flow when the shower valve's set to hot to activate the switch?

 

[murphs14]

The flow rate is poor anyway. It is a flat with the cold tank above the hot tank in a cupboard hence the pump. I realise I really need a negative head pump but they are so dear. It always worked if you put the shower head in bottom of the bath, then turn on the water. The pump would then start. Then you put the shower head up on the wall bracket and have a good shower. No problems. Now the problem is that the pump will only start if the mixer is on full cold. As soon as you adjust the temperature control toward hot the pump stops.

 

[longdogs]

Do you know you can buy pneumatic buttons for certain pumps with negative head?