air lock mains flush

Have a header tank and hot water tank. Turned off cold mains in and drained both as wanted to fit isolation values in downstairs toilet. There was no apparent isolation value on the hot tank out. Did job and turned mains cold back on header tank fills but hot water tanks doesn't (provides a...

I have always had issues with my open-vented CH (posted here in 2009). Radiators take ages to heat up, particularly two large radiators downstairs. Eventually heat gets to them, but the return is luke warm. I suspect an airlock on the return. Boiler recycles frequently. I gravity flushed and the...