Shower pump woes

[SecurityMark]

I'm having a mare with my shower pump in newly installed wetroom and would like some advice.

The setup is a salamander Ct75 2 bar pump sited on floor next to HWT supplied from hot tank via a salamander s valve (uisng about 1m of 22m piping), cold from new large loft tank again in 22mm. Pump connects to a thermostatic mixer via about 4m of 22mm, swept up and over the hot tank and down to the mixer.

After completion, all was well for about a couple of weeks then I noticed that turning on the water flow on the mixer wouldn't start the pump running until you reduced the mixer thermo setting to colder, increasding it back to a normal setting once running.

Yesterday, on trying to use the shower a second time it wouldn't start at all, even when dropping the thermo setting lower.

The pump runs fine once started and when stopped there is plenty of pressure into the mixer (loosened off the mixer inlets and it spurts out).
I've opened the mixer up and it appears that the internal NRVs in the mixer are sticking and aren't opening when the mixer flow tap is switched on, and as there's then no flow the pump won't self start.

Any suggestions - I've tried cleaning out the NRVs and it works first time but then once they close they won't re-open - would you suggest removing the NRVs and blanking off the holes with caps. What function are the NRVs doing in this configuration.

Could the problem have anything to do with the over swept feeds to the mixer from the pump, possibly creating an airlock????

Its a real pain having to strip down the NRVs before using the shower each time!!!!!

 

[ChrisR]

I've thought and asked and thought and wondered about a good reason for nrv's on pumps where both sides come from the same header tank.

No convincing answers, so a growing collection of nrv's removed from mixers. They're always horrid little resistive things anway - if you want you can add big low resistance ones to the pipes.

Maybe someone will dig out a water reg, but since they aren't connected to the mains, why?

If you're feeling rich change the pump for a negative head type.

 

[SecurityMark]

Thanks Chris

Replacing the pump is last resort, can i get by with just drilling out the NRVs from the centre of the cap and refitting. i'm happy to do it but would like some reassurance that I won't screw something else up b4 i get me drill out as once its done its done.

Why do they fit the NRVs anyway as the pump maintains a pressure when off.