Shower Pump Pulsing...

[OldJake]

... but only immediately after you turn the shower off.

We've just moved into this house and the shower has a Grundfos STP 4.0B shower pump. Fed from a large tank in the loft from what I can work out, and going to a thermostatic shower.

The shower works perfectly when you're using it. But when you turn the shower off, the pump pulses about once a second. It might do it 3 times, it might do it 20 times and then it stops.

If this isn't normal, has anyone got any idea on why it's doing this, please.

Thanks in advance!
Andy

 

[Exedon]

From memory that's a positive head pump
First thing I would check is correct working of reed switches they are clipped to pump outlet.
If your in a hard water area could be flow switch itself.

 

[OldJake]

From memory that's a positive head pump
First thing I would check is correct working of reed switches they are clipped to pump outlet.
If your in a hard water area could be flow switch itself.

Thank you. I'll have a look. We *do* live in a hard water area but the supply has a water softener (big thing that eats about 5kg of salt tablets a week)

 

[Madrab]

Does the pump run anything else or just the shower?

If the pump is hunting then it could also be down to water movement in the pipework due to the sudden shutting off of the valve and the concussion wave is traveling up and down the pipework to dead ends, drips etc and it can take a little time to settle down.

 

[OldJake]

Does the pump run anything else or just the shower?

If the pump is hunting then it could also be down to water movement in the pipework due to the sudden shutting off of the valve and the concussion wave is traveling up and down the pipework to dead ends, drips etc and it can take a little time to settle down.

It's just the shower that it runs. I might try slowly turning the shower off. I tend to turn it off as fast as I possibly can to avoid getting blasted with cold water.

 

[Felix247]

We have the 3 bar version of the same pump. After 12years of service it started doing the same thing, but continuously until powered off at the switch for a few seconds. Fitting a (full bore) non-return valve on the outlet pipe fixed the issue.