shower pump pulsing on and off

[bobjayes]

Hi guys wondering if you can help , I've a salamander esp cvp75 pump feeding a wash basin and shower in a en suite in a loft conversion. The pump is feed from a hot and cold tanl sited in the loft along with the pump. the pump runs in negative head mode as the shower head is above the cold water tank but the wash basin is below it. The problem is that the pump runs fine when the taps on the wash basin is turned on. When the shower is turned on the pump starts runs for 5 secs then stops for a second the on for 5 secs then stops , this cycle continues as long as the pump runs. The weied thing is that as soon as I turn the tap on in the basin , be it a very small amount the pump then runs fine.
Spoke with salamander who asked me to confirm no non reurns valves are fitted on output which there isn't and the pressure in the pump is set ok which it is. They now suggest it's the thermostaic shower mixer which it is'nt as I've swopped it out for another unit and the problem is still there.
Any ideas welcome before I consider last option of changing the pump,
many thanks

 

[charliejamesuk]

I came across a similar issue the other day, a Watermill pump and two Grohe showers. Pump manufacture and shower manufacture say it has to be the filters or non-return valves on the shower with the issue.

I've passed this onto the customer and am waiting to see if they wish to proceed further with the investigation.

 

[shaky]

Try putting non return valves on the outlet iv had this problem put non return valves on and now all is ok

 

[bobjayes]

Cheers guys for comments, I've checked the inline filters on the shower mixer ,blown though the mixer , check the NRV on the mixer and alls well. Salamander insist there should not be any non return valves on the output of the pump as the ECP CVp has them built in. It's a mystery and I'm considering buying a stuart turner neg head pump, but part of me says try to resolve problem just in case it's not the pump. I've even tried changing the pressure in the pump , higher and lower and the correct setting still the pump pulses.
Logged another call with salamander but as of yet no reply,
regards