Central heating not working after vavle change

[Paul-the-Pen]

Head scratching time. I have ana Ideal Classic boiler system that has a header tank and the radiators will only work so long as the water is being heated and the bathroom rad is always on - I don't know the technical name for that kind of system.

Anyway, I had a leaky thermostatic rad valve that needed replacing so drained the system, replaced leaky valve and filled the system again, bled the radiators switched the room thermostat in the hall up full,put the boiler on a higher setting (number 5 instead of the usual

3, and switched the boiler on using the timer.

The water is heating and the bathroom radiator is hot but ...... the boiler doesn't stay on for long and the rads do not warm up - none of them, including those without thermostatic vavles. I can't easily access the pump becaus ethat means ripping up the bathroom floor! so not too keen on that idea! I think I can hear its motor werring when I switched the boiler on.

I left it for half an hour but nothing only the water heats - any ideas welcome

[Invisible Man]

Is it a system where the hot water is heated by a non-pumped loop and the pump turns on to push the water round the radiators?

Could possibly be that muck in the system gathered in one place and is causing grief. Far, far more likely that you have an air lock somewhere in the system. I have a nightmare getting the air out of my system every time I drain it down. Any valves other than on the radiators you can try opening? Any joints in higher areas you could carefully loosen off a bit? A few towels on hand is advisable!!

Be careful running the pump too long. It may be full of air and not have any lubricating water in it.

[Paul-the-Pen]

I think the pump only works the rad heating not the water heating. I used a system cleaner before draining and surprised how clean the water was coming out. I flushed the system a few times before fitting the new TRV. I am beginning to think that perhaps there is an airlock in the pump as it seems likely to me that if air is stuck in there the motor would make a noise but not circulate the water

Does that sound logical?

[YAPH]

Sounds like air in part of the system preventing proper circulation. First off I'd look for air-bleed valves around the pipework in the airing cupboard or any high points on pipe runs. If there's nothing you can bleed it could be an air-lock in a pipework run, which can be a right pain to clear: I've resorted to connecting mains to the vent pipe so water gets forced back up the feed into the F&E tank and out via the overflow. This can also clear blockages where muck has gone down the flow pipe as the header tank emptied.

[Roger Mills]

Yes, it certainly sounds like an air-lock. One thing to try is to give each radiator a really good bleed - one side at a time. That is, bleed with one valve closed and the other one open - then swap round. That way, you ensure that both the flow and return pipes are full of water. You'll need to bleed out a litre of water or more with each valve open to ensure that the pipes are full.