Pump makes strange whooshing noise

[TeeKay]

The pump in my system boiler has suddenly started making a variable whooshing noise like you get after a fill when the water has lots of air in it and you can hear the pump cavitation. Infact it sounds more like a dishwasher than a heating pump.

I'm pretty sure there is no air in it. It is a sealed system and the last time I added any water to it was about 3 years ago after removing a rad to decorate. The highest radiators in the system have no air in them and the the auto air vent by the hot water tank is hot right at that top indicating it has water in it, not air.

The pump (head) is a Grundfos 15-60 and it is about 12 years old as is the boiler. I don't want to replace it unnecessarily, and I can't think of what would suddenly cause it to start making this noise. There are no other symptoms as far as I can tell.

Anyone got any ideas?

 

[misterdubya]

Firstly, I would check the header tank or system pressure at first - when you say 'added water', do you mean re-pressurisation?

If you do have a header tank and it's not dry, I would suspect a blocked cold feed pipe.

 

[TeeKay]

Sorry - I should have said - it is a sealed system. The pressure is about 1.5 bar. Have updated original post.

 

[Boilerman2]

Is the pressure Guage working or is it stuck at 1.5 bar, try giving the gualge a gentle "tap" and watch that needle fall to 0 !!

 

[TeeKay]

Boilerman2 - I expect it won't suprise you to know you were right
Well almost right, when I got home to check the pressure again it was now displaying zero!

Re-pressurised and holding its pressure and no noise now. Thanks very much indeed for your advice.