You probably have an air lock, try holding down the ball valve in the tank until the tank is full to the overflow, then try bleeding the radiators.
If this is unsuccessful try opening the drain valve again with the mains on.
[quote="Simon39"]Followed instructions for draining down system (open vented) and when I switched the mains water back on, the header tank has filled but is not supplying water beyond this back into the radiators?
Any help much appreciated (freezing cold and a 4 and 2 year old with no heating!)
I am not a plumber but have you opened rad bleeds at lower level then let it bleed and then open bleeds on top level sometimes air stops water flowing if bleeds are shut it happened to me once hope it helps
one of two things can be done. blow as hard as you can down the vent pipe that is curving over into the F&E tank until bubbles come out through the bottom of the tank OR attach a hose that is connected to a mains tap to the same point and pulse water through until the tank starts filling in reverse and that should clear your blockage.
It does sound like there must be a bit of silt in your F&E tank (possibly years of neglect!), my advice is maybe clean it out, flush the system through a few times both hot and cold to clean out any major deposits in pipe work, scoop out any major deposits from the tank (empty of course via the iso valve) and then add an inhibitor, something like sentinel x100 into the F&E tank whilst refiling the radiators.
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