Air lock

Old 09-28-04, 03:27 AM
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Air lock

I have a standard heating system with an indirect hot water cylinder heated from a gas boiler, with the cold water supply for the hot water coming from a header tank about 9 feet above the outlet from the cylinder to the hot water taps.

This has always worked fine, although anytime the system is drained it takes ages to get rid of the air locks. However, we have just moved the cylinder about 10 feet to a new location the other side of a hall and have a real problem with getting the hot water to flow. Apart from extending various pipes to allow the move, nothing else has changed, but the hot water flow is very slow.

The odd thing is that I can hear the water from the header tank trickling running down the pipe which feeds to the bottom of the cylinder and I think that there is some air lock which is preventing the head of water from pushing the hot water out of the cylinder in anything but a trickle.

Is there any way to try and clear this? Thanks.
Old 09-28-04, 01:24 PM
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sometimes cycling the pump can get the air to move on for you. or get the pump to start pumping again. try turning it on and off several times to get some movement in those pipes. you should be able to hot wire the pump so you dont have to turn the entire system on. just the pump. also you did not mention bleeding the air off. do you have bleeders and have you already attempted to bleed the air off. I would think that the cylinder has a bleeder on it somewhere. is this the case. it could be hiding on you
Old 09-29-04, 01:07 AM
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Thanks for the reply. However I think I have mislead you on which pipe I am referring to. I have put a picture here: Cylinder

The pipe entering the bottom of the cylinder is the cold water feed from the header tank. This water comes out of the top of the cylinder as hot water to the taps, via the other 28mm pipe that you can see. (you can just see the two pipes from the boiler, lower left, which heat the water via the heat exchanger inside).

It is the cold water feed to the bottom of the tank which is air locked, which I find odd since it is such a large pipe. However, it also occurs to me that if the cylinder, which is about 25 years old has a load of crud in the bottom, maybe when we moved it, it has partially blocked the inlet. You would have thought that 9 feet of head pressure would clear it, but maybe not?

Any thoughts? Thanks.
Old 09-29-04, 10:07 AM
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It would work much better if your circulator was on the supply instead of the return. Is there a dedicated circulator for the indirect? If so, perhaps you could put it in the supply. If not, you will probably need to put a valve and drain tap in so that you can purge that air out.


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