Ideal Standard Boiler airlock or CH pump failure?

[culky]

Can anyone help me diagnose this - I'm not sure where to go from here other than shelling out on a new CH pump in the hope thats where the problem lies...

Last night the CH system developed a leak upstairs. Judging by the size of the puddle (large) and the rate at which the water was escaping (a dribble) , I'd guess that it was whilst the system came on in the early hours of the morning and had been undiscovered for about an hour.

I drained down the system and made good the leak. I then refilled and bled everything twice - radiators,pump, the vent/bleed above my HW tank.

Now when I switch my boiler on (An Ideal Standard Classic non-combi) it lights for between 30s and 60s before switching off. I've checked the pumped flow pipe from it and this gets very hot. The return into the boiler stays cold. Its as if the boiler is heating static water and the thermal cutout is coming in to effect.

I've checked the CH pump (by ear) it's running but quiet so it doesn't *sound* as though the bearings are damaged. As the boiler brings the water up to temp i can hear some gurgling in the boiler pipework - the return i think. I dont know if this is sluggish water getting boiled by the boiler or trapped air trying to move though.

Could it be a trapped airlock in the pipework (If so, how can i expel it?)

or is it possible that the pump bearings are quiet but its somehow damaged by the leak enough to be unable to shift the water?

Any help gratefully received. I don't want the hassle and expense of replacing the pump unneccesarily..

All the best,
Darren

 

[ArtfulBodger]

Why not take the pump off and then open the valves a bit and see what comes out? it sounds like you've done everything right so far.

 

[felix]

First question: Are you sure that pump's turning. Induction motors hum even when stalled. Look for a knob on the back. You can usually unscrew this, pull it out a little to engage it in the shaft and turn the thing by hand. Do this with the pump off.

If you're quite sure that the pump is turning then you're left with the airlock theory. Do you have a three port valve, or indeed any other kind of motorized valve. These should be in the open position while you bleed the system. A three port should have a little lever on the side for holding it in the midway position, ie both sides open.

PS: Don't forget to release that lever afterwards or your radiators will heat up when you only want hot water.

 

[croydoncorgi]

Don't forget to release that lever afterwards or your radiators will heat up when you only want hot water.

manual lever (on most common valves) will release automatically when the valve energises.

If you PARTIALLY drained the system originally, there may well be airlock(s).
Quickest solution may be to FULLY drain it, then refill and bleed rads starting at the bottom. A possibly-useful technique is to bleed the ground floor then run the pump with the boiler off for a few seconds to kick air out of horizontal pipes and into radiators, then turn it off again and complete the bleeding upstairs. How easily a system fills up depends a lot on the pipe layout - but you obviously knew that!

PS Don't forget to add Inhibitor when it's all working again!