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indirect system, radiators red hot but hot tap stone cold

Postby Dave10001 » Wed May 06, 2009 7:39 am

leaking radiator valve forced me to drain (indirect) system.
Valve changed and now that I have refilled the system, there is only cold water coming from the hot taps.
The flow from the hot tap is as good as previous, the radiators are red hot, but the pipes around the hot water tank are all stone cold.
I have tried forcing the cold water back into the hot water tap (mixer tap) several times but no joy.
Any help would be much appreciated, thanks.
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Simply Build It

Postby Dave From Leeds » Wed May 06, 2009 10:31 am

Hi Dave,

You probably have an airlock in the heating coil inside your hot water cylinder. Two possible things to try.

First, find two pipes going into one side of the cylinder one directly above the other. Then slacken, but do not remove the union on the top one. This may allow the air to be pushed out by the head of water in your central heating top-up tank in the same way as bleeding a radiator. Once water starts to dribble out as well, wait until any air bubbles subside then re-tighten the connection. This may well solve your problem.

If the above doesn't work, a more complicated method would be to locate your CH top-up tank (F&E tank) This will be the smaller of two cold water tanks probably in the loft, but certainly higher than the HW cylinder. Fix one end of a hosepipe over the open end of the vent pipe that goes over the top of the tank with the other end attached to a mains water fed cold tap. Then get an assistant to slowly open the tap whilst you observe the tank from above. Air bubbles should come in through the outlet at the base of the tank. Once these stop, turn off the tap and all should be OK. Do not open the cold water tap too far or the flow of water up into the F&E tank may be too fast for it's overflow to cope.

Hope this helps.
Dave From Leeds
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Postby Dave10001 » Sat May 09, 2009 2:33 pm

Thanks for the advice.
Didn't have an adjustable big enough to crack the join so had to try the second option and it worked.
Fortunately the expansion overflow pipe is 22mm and so the hosepipe fitted nicely with a bit of ptfe tape and masking tape to create the seal.
Took it very easy with the flow on the first attempt but nothing happened (no bubbles); realised that there was not enough flow.
So second try gave it more flow and saw bubbles coming through. Then tried twice more and gave it max flow, tap on full.
Saw plenty more bubbles but suspect this was the air in the top of the pipe.
However it was worth the effort in the end.
Thanks very much for your help.
Much appreciated
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