Grundfos MQ3 making clunk noise and pulsing on/off when in use

Altheus

Video of it here, and you can hear the noise/pulse clearly - https://www.youtube.com/watch?v=JpHkEHTymc4

I drained the inlet to see if there was gunk or build up, but nothing .Basically after around 3/4 years of perfect service, my pump has started to stop/start when it's on. What I've checked:

- Inflow comes from attic tank which is full, no issues there. Drained it and no debris came out

- Outflow splits between feeding combi boiler and cold taps - issue happens on both feeds, again no difference.

John.G

Is it a variable speed pump?, a flow switch normally starts/stops these positive head pumps, there are green lights in the pump display, the center one goes on/off (video) with the pump stop/start, can you say what these lights are labeled, also, maybe have the outlet freely flowing to drain and see if pump stops. Check for any mesh type filter at the pump inlet.

Cyloncity

Not much knowledge here but is it possible a toilet cistern is not filling? If there's one connected. Hardwater areas could lead to build up on the cistern valve.

Altheus

Sorry so the pump turns on when it’s meant to - it’s not like a leak where pressure is dropping - it’s the opposite - it’s power cycling when it’s meant to constantly on.

The light for power on turns off and on again like you’ve turned off the tap - but no alarm. Leads me to believe that maybe it’s confused and think theres pressure in the system.

Cyloncity

Hi just wondering did you ever resolve this? We have a similar problem with our own pump now. Thanks