Secondary Return Pump kicking in and out (with video)

[alpesh26]

I have an unvented cylinder with the secondary return "circuit" plumbed in on the hot water side with a Grundfos Comfort 15-14 BA PM pump attached.

The issue I have, the pump is 'pulsing' so it runs for a second or two, stops for a second, then repeats this. Sometimes, it makes a slight squealing noise. It does this no matter which mode I put it on.

Video of issue: https://1drv.ms/v/s!As19bM4LfI6tkTr3-d02JHzAgUtq?e=9OjgZR

Any ideas what could be causing this behaviour? My understanding is that the pump should just run constantly. There is a check valve on the flow side.

TIA

 

[coopersim]

That sounds like it’s running dry?

 

[alpesh26]

Could well be, i checked the gate valve below the pump and it seems getting stuck. Put some WD40 on it for now, any tips on freeing it up?

 

[coopersim]

Is the pump new hence the gate valve having stuck when you closed it to install the pump?

It might be worth changing those valves out for something like a butterfly valve as they don’t tend to cause issues when you need to use them in the future.

if it were mine I’d want to check for the presence of water at the pump and check that double check non return valve is installed in the correct orientation and hasn’t gone bad.

I suppose the obvious question is what’s changed recently?

 

[alpesh26]

The whole system is new but the house has been empty for a bit so its only been now ive been able to test it properly. I managed to free the valve but i'm not 100% convinced its working because the spindle doesnt move out as much as the valve above it. Never been a fan of these gate valves.

Removing the pump will be a pain because of the pipes but I agree with checking whether water is actually getting to the pump. the pump isnt getting that hot which I would expect it to if hot water were running through it

 

[alpesh26]

To update this one, the gate valve below the pump was stuck so the pump was running dry. Leaving the pump off with the WD40 on the gate valve for a couple of days it eventually freed. Pump is now running almost silently and its getting warm as the hot water is passing through it .