Hope you can help, I woke up last week with no heating. I have a Baxi Bermuda 551 back boiler with gravity fed hot water and central heating is pumped. I still have plenty of hot water coming from taps but no rads (upstairs and downstairs), I have five pipes that are connected to the boiler: 2 X 28mm that both feel hot, 1 X 15mm that feels cold and 2 X 22mm, one with the pump on in the up direction that feels hot and one with the valve on with that feels cool, I called a plumber in who advised me it was a non return valve on a 22mm pipe. I drained the system down and replaced the valve in the same direction as the previous valve. Still no heat in the rads, have replaced and vented the pump. Still no heat in rads.I then put a Fernox sludge remover in the F & E tank, ran for a day then drained and vented again, to my surprise when I started draining the system the the top rads started getting warm. I refilled the system and turned the heating on and it was cold again. I'm confused that both the 22mm pipes seem to be coming from the boiler,thought it would make more sense that there ws one from (flow) and one to (return)the boiler, please advise.