Noisy Grundfos 15-50 Heating Pump?

point3

Right... I shut off the cold water mains supply over the weekend whilst changing a leaky basin mixer and a shower cartridge. Now, I'm beginning to realise that the central heating pump is scarily noisy. It sounds like the rushing noise that occurs when the system is refilling after using the taps or the loo, but it's on all the time! Have I invoked the wrath of the heating pump by leaving it on without a water supply for too long?

It's a sealed system - Glow Worm Energysaver 40e condenser boiler, Heatrae Sadia Megaflo Indirect cylinder, Grundfos 15-50 pump, expansion tank next to the water cylinder and Danfos controls.

I've recharged the air gap within the water cylinder as per the label's instructions.

I've topped up the expansion tank so that the pressure gauge reads 1.2bar (it was dead on 1bar before I let in a trickle of water ). The expansion tank doesn't feel like it's got any water in it tbh - just feels tepid all over unlike the adjacent pipes which are hot.

Is it time to call out Corgi Man to the rescue?

alanobrien

Sounds like the pump is cavitating i.e. air is trapped around the impellar or the seal is running dry (assuming it has one some are sealless) Is there any vent connection at the top of the pump you can get to ?

espresso

Have you tried bleeding the pump?

point3

Thanks for the suggestions. Much appreciated.

I went and had a look and couldn't see anything resembling a manual air vent, only a safety pressure release valve above the expansion tank.

I switched off the pump and tried bleeding it, but it's made no difference. Still making a roaring noise and an intermittent whistling noise when you get up close as well now. Oh dear!

Canucklehead

Hi

Air gap in the Megaflo is on the domestic HW side and will not affect the c/h.The same applies to the changing of the basin tap and shower cart.

External red expansion is the c/h and sounds ok at 1.2. It will not get hot.

A sealed system will clear air very quickly.
I wonder if the pump is failing and not circulating the water fast enough, the boiler is heating up the water to near boiling producing air bubbles.?
Is it air or is it gas from corrosion in your system.If you vent a rad is the water very black?
Is there any thing different about your system that you haven't noticed before?
Is there an automatic air vent on the pipework (at a high point) is it allowing air in?

Can't think of anything else.

Corgi Guy.

point3

You're right. The CH circuit shouldn't have been affected by the changes on the HW circuit, but as the problem sounded like turbulent water flow I thought I'd better check both!

Could be a pump problem and I'll get someone in to check that if there's no improvement...
I vented the radiators to check...the first one in the bathroom had a dribble of black water and then clear. All the others had clear water.
Nothing different noticed, as far as I can tell.
There's an automatic pressure release valve above the expansion tank - the overflow to this has an air vent below the level of the tank.

Hot water and heating still work, so the situation's not desperate. Hopefully it'll just be a case of fitting a new pump...

Thanks for your suggestions