Air lock in Gravity HW - cant shift it!

[mk2phil]

Hi there,

I've got a 'C' plan CH/HW system. I recently drained the system down to have some plastering/painting done. Refitted my rads and refilled the system as normal, however the HW side isn't heating up at all.

When I've drained and refilled before, this normally always happens but soon clears itself within a few days, but this time it's taken over 2 weeks and still hasn't sorted itself. I've tried running the boiler on HW only for a good 4 hours, boiler truned up to max, but still no joy. Some of the rads in the top part of the house are heating up (through gravity I assume) but the inlet/outlet on the tank asre stone cold.

Yesterday I thought i'd try the method described on here - boiling up the boiler. removed the stat from the boiler, let it run until I saw it overpumping into the F+E tank in the loft, at which point I switched the boiler off. Went and felt the inlet/outlet pipes on the HW tank and they were boiling so I had assumed that the water would have pushed the air out on its way. Refitted the stat and ran the boiler HW side only again hoping that it had sorted the problem but no! Still cold!

I thought that I'd only need to get the boiler to overpump once for the air to be pushed out? Do I need to do this more than once?

Or should I try draining some of the system down again and hope that when it refills this time, the air gets out as it has done previously before?

Any help much appreciated.

Thanks

 

[combispecialist]

U need 2 chk 2 see if u have a blocked cold feed,boil it up a couple more times,if that fails ure cold feed is blocked

 

[mk2phil]

Dont think it's a blocked cold feed as the CH side fills perfectly. When I see it dump a load oh water into the F+E tank, is that effectivelky boiling over - i.e. it's reached approx 100 degrees, boiling and therefore forcing it out of the overflow. I suppose what I'm asking is have I got it hot enough when I see it dumping into the F+E tank....? I dont want to damage the boiler by letting it get too hot.

Thanks

 

[Nige F]

Dont think it's a blocked cold feed as the CH side fills perfectly. When I see it dump a load oh water into the F+E tank, is that effectivelky boiling over - i.e. it's reached approx 100 degrees, boiling and therefore forcing it out of the overflow. I suppose what I'm asking is have I got it hot enough when I see it dumping into the F+E tank....? I dont want to damage the boiler by letting it get too hot.

Thanks

If it`s a conventional gravity circuit to the cylinder - the cf. should be in the return by the cylinder and the vent in the flow above and done in 28mm pipe .

 

[combispecialist]

Waite for the loud rumble thru the pipes then turn the stat off!yes if its shooting thru vent pipe then its boiling over.do it a couple of times then it will shift eventually.

 

[stumpydick]

connect a hose [using reducer] onto open vent and give it a blast of mains water. watch you dont overfill f/e tank .