Rainfall shower pressure problem

[the chippie]

Hi we have a rainfall/riser shower fitted over the bath, on a agravity fed system. We have 2 showerboosterpumps under the bath which supply the hot water in the kitchen below and the bathroom hot water. The problem is the shower won't kick in when turned on, pressure is good on all other taps

 

[ShaunCorbs]

Need a universal shower pump and not a positive one

 

[the chippie]

Thanks for the response, the cold water tank is in the loft so higher than the the shower, doesn't this mean it's positive head?

 

[John.g]

A positive head pump needs a minimum flowrate to activate the flowswitch to start the pump, a universal/negative head pump uses a pressure switch with a mini expansion tank to start the pump. If you open the bath hot tap then you may get enough flow to start the pump. I have been in showers where you have to put the showerhead on the ground to start the positive head poump but not so easy with a fixed rain shower.

 

[SimonG]

Universal or negative head pump as above. In the meantime open a hot tap when you want to use it.