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radiators hot but no hot water after draining system

Postby plumbhome » Tue May 12, 2009 10:09 am

hello i have an indirect system and after draining the system down to install new basin & bath taps(no iso valves!) i had an air lock on the cold basin & bath feed. the kitchen cold feed was fine though.

i fixed the cold air lock using the garden hose & round tap connector to the basin, to push the air throught the vent pipe in the loft. job done.

but still no hot water, the rads are piping hot but the hot taps are running cold. i take it theres an airlock in the dhw feeds somewhere?

the boiler is situated right next to the cylinder upstairs.

how do i tackle an air lock on domestic hot water? same method as cold?
any help would be much appreciated.
Thank you
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Simply Build It

Postby Dave From Leeds » Tue May 12, 2009 4:34 pm

Hi plumbhome,

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.

Someone else recently had this same problem and fixed it using the second method. Good luck.
Dave From Leeds
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