Intermittent Noisy central heating pump

[SukhyB]

Need some help please.
I have a Grundfos Alpha2 Water pump and over the last few days it has started to make a deep vibrating noise. At first I took the air out of the rads and I thought this would resolve the issue but is has not. The noise remains and it is intermittent in that it might be noisy or it might not be. Or it may start fine and then turn noisy. It is running on level 3 but obviously turning it down just takes longer for our rads to heat up. So the pump seems to be working in that our rads are coming on fine. Need some help at what the issue is?!?! If it was the pump and say the bearings had gone then I would expect it to be noisy all of the time.?!? Help would be appreciated! Thanks.

 

[75pete]

Try bleeding the pump and reduce the speed

 

[SukhyB]

Thanks for your message. The pump cannot be bled. Grundfos tell me it is self ventilating and there is no screw to let any air out.

 

[oilhead]

Intermittent noise is symptom of air locks. Bleed the pipework as close to the pump as you can get, on the inlet and outlet, and move progressively further away.

 

[Gasguru]

If its on a sealed system is the pressure ok, if an open system is the feed and expansion cistern filled with water.
Do the rads repeatably fill with air?

 

[SukhyB]

Intermittent noise is symptom of air locks. Bleed the pipework as close to the pump as you can get, on the inlet and outlet, and move progressively further away.

Thanks. I will try this again.

 

[SukhyB]

I have an Open system. Yes the feed and cistern is filled with water. I will check the rads again to see if there is air in them. Should i check just the upstairs or could it be downstairs rads too?!?

 

[ianmcd]

Turn everything off and see if you get a steady stream of water out of the bleeding vent of the highest radiator/towel rail in the system

 

[oilhead]

A steady stream out of the top radiator does not necessarily mean you have no airlocks. Whilst the boiler is running, do all the rads get warm? Are you getting hot water?

 

[SukhyB]

Hiya. Yes, all of the rads get hot.
Will check the rads again for air and will let you know.

Thanks all for your advice.