Hot water booster pump: on but not boosting

[johnny366]

Hi
I have a pressure activated hot water booster pump in my loft bathroom. It's worked fine since installation but after some recent repairs to the bathroom, it no longer works properly. It switches on when the hot tap is opened, but makes a loud dry rattling sound, and no water is pumped. After a while (a minute or few) it might kick in and then function properly, without interruption. Video here: https://goo.gl/photos/2KsLVVJJwf4LotLx7
Airlock maybe? Can anyone advise?

 

[PrenticeBoyofDerry]

As mentioned, maybe an airblock. Can you vent/bleed the pump.

 

[Agile]

Just possibly the impeller might be loose on the motor shaft but sometimes catching and operating.

Tony

 

[johnny366]

Thanks gents,
I think Tony, that might explain the noise like a roulette wheel...! Maybe replacement due then.