I have an old open heating system with a header tank in the loft. I part drianed the system last week to repair a valve. Once i truned the system on again the upstairs rads would not fill up. tried to bleed the rads but no luck. Completely drained the whole system and now it will not fill up at all. So no hot water or heating. The header tank is still full in the loft. I thought maybe an airlock but if completely drained how can this be the case? Any ideas greatly appreciated.
It is not unheard of for the feed pipe between the header tank and heating system to become blocked with sludge. Try unblocking it with a plunger or connect a hosepipe to the pipe to unblock it. But bear in mind it may be difficult to remove.
I have come across this problem a few times, what i have done to over come this is to get a lenght of hosepipe put 1 end into the tank against the return pipe and blow realy hard down the other end this usually pushes water down the pipe and shifts the sludge or air block, if that does'nt work get a hosepipe connect it to a cold tap put the other end tight against the return pipe in the cold tank and switch the tap on, the pressure will deffinetaly shift the block, it's always worked for me, good luck