Airlock problem to hot water tank?

2 Apr 2005
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United Kingdom
Gravity heating system, with Potterton boiler, central heating works fine, but hot water side appears to have an airlock. Feed from boiler up to hot water tank is very hot, so water being pumped up okay, but exit pipe from the hot water tank is it isn't flowing through, and therefore not heating the water in the tank. Note this is not the hot water being supplied to the tapes, the problem is in the pipes carrying the water that heats the water in the tank.

About 12" from where the lower pipe exits the hot water tank there is a 90 degree, downwards elbow, which is sometimes home to an airlock. Swift tap on the pipe usually sorts this, but today I can't seem to shift it....does anyone have any suggestions?

Have checked motorised valve - working fine, and I know the thermostat is working because the boiler is firing up.

Someone suggested I try turning the hot water tank thermostat to max, with the heating switched off, to see if this cures it - bit wary of this approach, how long do I leave it to see if it clears the problem?

Any advice much appreciated !
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Is there a gate valve fitted on either the flow or return of the cylinder?
No gate valve on either the flow from the boiler or the one feeding back to the boiler.

Where does your cold feed pipe enter the system? Usually it's a 15mm pipe tee'd on the return pipe from cylinder on a gravity system. Could well be blockage here, check tank is full in loft.
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Cold feed is teed, but on the pipe feeding into the cylinder not the return pipe. Have just checked the header tank, it's not empty.

I would suspect blockage in or around that area, when you previously tapped it believing it was air this may have dislodged it partially thus making it work again. Try a magnet on the pipework near the cold feed and see if it sticks.

Difficult without seeing it i'm afraid you may need to pick that damn phone up and have someone clarify problem further.
Thanks for the input Gas2Air, I'll try the magnet and see what happens. Thought I would give the forum a try before I ring a plumber :)


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