My system is gravity fed hot water with pumped central heating. I drained the system down a few weeks ago to replace a radiator. Since then I don't get any hot water although the CH works fine. I presume that there is an air lock somewhere as the hot water tails are hot at the boiler but are cold when they reach the airing cupboard. The feed pipe into the hot water cylinder (higher of the two) runs up at a 45 degree angle from the junction with the open vent. If the airlock is in the coil inside the cylinder, is this angled feed stopping the air from reaching the vent? Should this pipe enter the cylinder in a downhill direction i.e. the air can escape uphill in the opposite direction?
check to see if your feed and expansion tank is full,sometimes when you drain down the ballvalve sticks in closed position,central heating side will work ok because its pumped,hot water requires sufficient head to help process of gravity circulation.Worth a look
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