Cant refill central heating system!

[Anonymous]

Hello - I drained the central heating system yesterday to replace a dodgy rad valve. I tied the ball c*ck up and unscrewed the drain valve that was conveniently routed outside.

To refill the system I turned all the rads off, released the ball c*ck and let the system flush through the drain c*ck until all the air passed through. At this point I closed the drain c*ck and turned one rad on upstairs and bled it. ( I could hear the system filling up through the header tank while I bled it.)

I switched the boiler on (with just one rad on), it fired up but five minutes later turned back off without the rad getting anything more than luke warm. My plan was to check this got nice and hot, and then move to do the same with the rest of the rads......

Its a 20yr old conventional system with microbore piping.

Any ideas, am I doing this wrong?

Cheers Russ.

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[Peter Ashby]

Put the heating on continually then you have to go around all the rads and bleed them all, starting on the ground floor then moving upstairs. You are trying to drive any airlocks upwards. You keep doing this until all radiators bleed only water.

I removed the large double rad in the hallway for painting recently, when I replaced it I couldn't get water out of all the rads, then there was no hot water... Turned out the ball had got stuck on the side of the header tank. I too have microbore. Once that was fixed and there was enough water, all was sweetness and light. You do have to do all the rads though, some more than once. Take pliers as well as the bleed key, some of those plugs will be tight.

Peter

[Andrew Gabriel]

You don't allow the boiler to fire up until you've got the bulk of the air out of the system, or you risk running the boiler with an airlock and wreking it. Often it's useful to run the pump without allowing the boiler to fire up (maybe by cutting off the gas supply -- depends on boiler).

[russ]

Because i managed to bleed the one rad successfully, I thought I had managed to get most of the air out? The boiler should work fine with just one rad connected, right?

I was thinking that turning all the rads on at once and trying to chase airlocks around would be more difficult than switching turning one on - bleed it - then move to the next one etc.. untill they are all on.

Since posting, i have actually tried turning all of the rads on, bleeding them (no air in any of them) and switching the boiler on, but the same thing happens - fires up for 5 mins then swithces off....

Thanks for the replies - appreciated!

Cheers

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[Autolycus]

It used to be fairly common practice to install the pump in such a position that the system was under negative pressure when it was running, in which case the pump must be off, or you'll suck air in at the bleed screws.

I agree with others that the general principle must be to open all main radiator valves (don't disturb the lockshields) and bleed all radiators before firing the boiler. If the hot water primary circuit is pumped, as it may well be, check for a bleed valve next to the hw cylinder, too. This may be an automatic one, but it may be stuck closed.

[russ]

Thanks for all the replies!

One more quicky before i give this another go - should the three port valve be moved to manual while refilling?

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[Heliotrope Smith]

Yes

[John Stumbles]

Does it lock out and need resetting or just turn off because it's got hot enough (even though the rest of the system hasn't)? If it's locking out it's getting too hot either beacuse there's air in it and it's getting very, very hot and eventually that's getting to the overheat thermostat or because there's insufficient circulation. If it's just cycling because it's hot enough then the water it's heating obviously isn't getting to your rads. Check for a bleed point somewhere around the hot water cylinder which may need venting before water can circulate properly.

[Lobster]

Might be worth now reverting to just having one single rad on, to force any airlock round the system by the increased pressure, but TBH I think that should have worked when you tried it originally.

Next up for me would be to force water into a drain c*ck as somebody else has suggested.

David

[Dave Plowman (News)]

It's the only thing that works for me, so I don't bother farting around anymore but go straight for it. To make life easier I changed the cheap and nasty drain c*ck which leaked round the spindle for one with a proper gland assembly - which also stops leakage when draining down.