Newly installed shower not shutting off properly

[Londoner]

I've just had a shower put in with a Salamander pump in the loft. It's been ok the last few days but tonight I used it and after switching off the shower mixer, I could hear the pump repeatedly powering up and down, as if it thought I was switching the shower off and on repeatedly. It didn't stay on continuously, but kept going on and off.

I switched the electricity off at the mains for a second, then on again and it carried on doing the same thing.

Then back in the shower, I turned the thermostat switch down to a lower temperature and that finally made the pump stop.

After a bit I turned the thermostat back to the original higher temperature, tested the shower and this time the pump stopped as it should.

Any ideas why this happened and do I need to get the plumber back in? This is only the first time it's happened but I wonder if it's a sign of a problem? Just what I need before Xmas!!

 

[ChrisR]

Are both supplies tank fed from the same height?

Could be some air in the pipes making the water bounce about - just!

Does the pump feed the loo too?

Is it a negative head pump?

 

[Londoner]

Are both supplies tank fed from the same height?

Could be some air in the pipes making the water bounce about - just!

Does the pump feed the loo too?

Is it a negative head pump?

The pump sits on the attic floor, next to the hot water storage tank. The cold water tank is on a raised platform, higher than the hw storage tank.

The pump doesn't feed the loo, no, just the shower. But the shower does have two heads though (overhead and hand shower).

Not sure about the negative head question!

Thanks for answering.