Persistent air-lock

Joined
6 Dec 2006
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Location
Cheshire
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United Kingdom
The last rad. of the upstairs circuit is a drop-feed to the lower floor
(solid floor!). Rad. valves are bog-standard, c/h pump is in the return to
boiler, system vented, all other rads. properly balanced, system degunged
and inhibited so water runs clear. No air collects in rads.

This last rad. persistently fails after a few days. I can clear it by
shutting the rad. c/h return and allowing a fast drain from the hot feed
(luckily I fitted a combined valve/drain-cock some years ago). After about 2
pints of the hot feed have run off there is a rattling noise in the local
feed pipe (air bubbles I guess). After this I can return things to normal
and this rad. will work for 2-3 days before failing again. I\\\'m getting bored
with going through this palaver :(

My guess is that I have an air leak in the hot feed pipe run between the
last rad. upstairs and the drop fed rad. The next move will be to shift
upstairs furniture, take up some floorboards and inspect this pipe run. But
before I set about all this I\\\'m hoping wise fellas here will advise:

Is this a sensible diagnosis or have I missed something obvious?

Would 35-year old soldered joints go leaky in this way - i.e air getting in
but, as far as I can see, no water coming out?

If all this is true I guess I will need to drain the system and remake the
soldered joints?
 
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Difficult for me to visualize pipe runs.

Upstairs rad feeds ground floor rad with drop pipe work? flowing down and rising up on the return.

Have you tried balancing the system from this problem radiator. In other words, working backwards towards the pump/boiler. restrict the flow to the other rads more. You may also have to increase the pump speed.

It seems to me that the drop and then rise is acting like a old fashioned water level and any amount of air circulating around the system will get trapped in this 'U', thus creating an air lock.

When you let water through manually as you describe you are probably getting it to flow again, until the next air plug comes round again.

I wouldn't have thought air would get in through faulty joints without obvious leak. :confused:
 

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