No heat/hot water, suspected airlock?

[chrisinbris]

Hi,
I've been having problems with heat circulating in my CH since I replaced a radiator in the bathroom about a month ago. System is a vented, pumped system with a quite old Concord WRS boiler (pump on this replaced last year, system also powerflushed at that time).

Everything was fine before the new rad, it filled with water fine but thereafter the heating was only sufficient to heat a few of the rads in the house at a time (there are four up, four downstairs). At first I assumed I needed to rebalance the system, but all attempts made no difference (I've successfully done this before). Next I assumed an airlock and let some water out from the stopcock downstairs for about half an hour from each side, feed and return. IF anything the problem worsened. This morning I drained the whole system and allowed it to refill but now I'm getting no circulation at all.

When I turn off the power to the pump I always hear water gurgling up away from the boiler. I also hear it when I turn it back on. Hence my assumption of an airlock. Of course I've tried bleeding from every available place, frequently getting air in the pipe by the hot water tank in airing cupboard. When the boiler is on it heats water for about three minutes then cuts out for about twenty. The return pipe to the boiler is cool, but I'm assuming there is some sensor in the boiler that cuts it off, even though that hot water isn't going anywhere. My other concern is that I"ve noticed that the vent pipe is just T'd off from the feed/expansion pipe in the loft. That's not how the diagrams in the books look.

How can I move this air? The one suggestion I've read and still I might try is temporarily switching the pump around to pump the air out the opposite direction.

Thanks for any help,
Chris

 

[cider]

You have a combined cold feed and vent which can make it difficult to initially remove airlocks.
Can you crack a nut down by the diverter valve (if you have one) in airing cupboard to release the air?

 

[chrisinbris]

The diverter valve (that switches between hot water and heating?) is on compression fittings so I guess it would be possible to crack one of those. I'm not sure if I understand though, on the hot water side there is a vertical pipe with a bleed screw on it (bleeding this hasn't helped me move the airlock) and on the heating side is the combined vent/feed expansion pipe. In theory I shouldn't be getting trapped air in that, should I? Today I am draining the system and back filling it from the bottom. Hopefully this will help because after that, I am out of ideas.

Thanks,
Chris

 

[Ronald0]

If the boiler thermostat is shutting down the boiler after 3 mins but the cylinder stat and/or room stat is still calling there is insufficient circulation.
Heat is not being drawn away from the boiler.

You have bled the hot water circuit upstand but have not mentioned bleeding the radiators. Are you still getting air from them? Have you bled the pump?

As the boiler fires, hold the pipes either side of the motorised valve. Can you feel the water temperature rise on both primary and secondary sides? Does the pump respond to a change in speed setting?

 

[chrisinbris]

I have bled everthing, all the rads (these never produce any air) and the pump. When I bleed the pump, water comes out accompanied by a hissing noise. Thinking that this hiss is some air, I've bled it for up to fifteen minutes at a time. Both times I tried this I gave up before the hissing stopped.

The pump is located in the boiler cabinet on the return feed just before it goes into the boiler. The feed side leaves the boiler hot, the return side is cold/cool. The pump whirs when it's on, and the sound changes when I switch through it's three speed settings.

In the airing cupboard the valve is not motorised. This morning no hot water was reaching pipe leading to the valve. I have drained entire system and refilled from the bottom, bled and turned on the boiler. Boiler still cut out after a few minutes, now the pipe near valve is lukewarm to touch.

 

[Ronald0]

Chris,

The boiler needs to run for longer. Is there a higher flow setting? If the return water temp is cold the boiler thermostat is cutting the boiler too soon.

Do you have the boiler manual? Can you disable the thermostat by linking across to force the boiler on longer?

 

[chrisinbris]

A quick follow up...

I drained the system down today and took off the valve switching between heat/hot water. The 22mm pipes in and out of this were caked with hardened sludge, so I cut out as much pipe as I could get access to and replaced it. Refilled and voila - heat and hot water restored. My guess is that the powerflush that I did moved all the built up crap in the pipes until the hit a restriction at that tiny valve, where it clogged and reduced the flow of water to pretty much nothing. It works now, thanks for the help.