Air Locks in CH

[Endulini]

Hi Folks,

Following a drain-down and refill of my CH system (for a biannual clean) I have a couple of rads that aren't heating up at all, I can feel the inlet pipes are hot/warm and bleeding the rads releases water (but no air) but the rads themselves are cold. I'm pretty certain it's not the TRVs as both were working before draining down.

One rad has a history of problems as it is on the end of a long (5m) horizontal pipe run in the attic but usually a full drain-down and refill sorts it out. This is in a bathroom and heats up when the hot water is active. The other rad is on the CH circuit but is usually quite reliable.

Both rads have drain valves attached and I have tried pulling through water whilst the pump is going to see if that pushes out the air.... (it didn't).

The system itself is generally a bit problematic as it mostly microbore pipework and I'm not convinced it get good circulation despite installing a larger pump.

Any thoughts?

[John Rumm]

Is this a vented or a sealed system?

[DerbyBorn]

Throttle down the radiators that get hot first. Work on the assumption that if you have say 12 radiators - the system will only feed about 8 if they are all full bore. You need to force the water to go where it isn't easy for it to go. It takes the easy option. Use the Lockshiled valves on the other radiators. They are to cause of the problem (unless you have a blockage - like I have on one)

[Endulini]

Hi Folks,

Following a drain-down and refill of my CH system (for a biannual clean) I have a couple of rads that aren't heating up at all, I can feel the inlet pipes are hot/warm and bleeding the rads releases water (but no air) but the rads themselves are cold. I'm pretty certain it's not the TRVs as both were working before draining down.

One rad has a history of problems as it is on the end of a long (5m) horizontal pipe run in the attic but usually a full drain-down and refill sorts it out. This is in a bathroom and heats up when the hot water is active. The other rad is on the CH circuit but is usually quite reliable.

Both rads have drain valves attached and I have tried pulling through water whilst the pump is going to see if that pushes out the air.... (it didn't).

The system itself is generally a bit problematic as it mostly microbore pipework and I'm not convinced it get good circulation despite installing a larger pump.

Any thoughts?

===

BTW, this is in a vented system.

[Tim+]

Change it to pressurised. Make bleeding much less problematic.

Tim

[DerbyBorn]

My system is microbore and I had 3 sluggish radiators. I only had a very slow flow out of one of the pipes when the radiator was removed.

I took the opportunity to have one re-piped when some ofther work was being done that exposed the manifold and the bare walls.

Turned out there was debris / crud in the union of the manifold where the Flow pipe was connected.

Unfortunately job was done whilst I was out and so didn't get the chance to ask the plumber to undo and clean the others. Ceiling now back and I am reluctant to do keyhole surgery.

Considering Electricians Draw tape poked up from radiator.

[DerbyBorn]

Tim+ wrote in news:ogjn7f$7mo$ [e-mail]:

Not convinced of that one unless it is so bad it is pumping over.

[Dave Plowman (News)]

Turn off all the working rads. This usually persuades the non working ones to start up again. Once they have, go back to normal.

[Alan Dawes]

Yes. I suspect that those 2 TRVs were blocked with "crud" when you drained down. What makes me suspect this is that although the water is warm coming to the rad it is not getting through the TRV into the rad otherwise that would become warm.

To check:

Turn off the TRV fully and open the radiator bleed valve, if water comes out then water is coming up through the "lockshield" return valve at the other end of the rad. Now close the lockshield fully and open the TRV if water dosen't come out then the blockage is at the TRV.

Depending on the type of TRV you could try removing the head and moving the actuator pin up and down (and perhaps spray with WD40) but I suspect you will need to replace it or at least remove it and clean it). Rather than draining down I've used the pipe freezing kits that you can get from Toolstation when replacing a couple of TRVs that had the same symptoms as yours.

Alan

[Dave Plowman (News)]

It did here, and mine wasn't. A pressurized system seems to have more consistent pressure all over - unlike an open one where there will be less head as you approach the tank level.

[tabbypurr]

+1. I assume you have a filter in the system, if not you need one.

NT

[John Rumm]

It definitely makes air lock and bleeding problems go away... (also reduces future corrosion)

[Roger Mills]

If there is air in one or other of the supply and return pipes, you won't get rid of it by bleeding the radiator with both valves open.

You need to shut one of the valves and bleed a couple of litres of water out and then open that valve and shut the other one, and repeat the bleeding operation.

If necessary, also do what others have suggested - turning off all but each problematic radiator in turn, and running the pump temporarily on its highest speed.

As others have said, converting to a non-vented system would make air removal easier - but if your vented system has worked ok in the past, it will work ok again once you've successfully bled it.