CH- airlock in pipes.

[entirelyuseless]

Open coal fire with large Baxi back boiler. 5 radiators which are all upstairs. None downstairs. Swept chimney Saturday, and everything fine until Sunday. Water got too hot and I now believe I have caused an airlock in the pipes. Water still gets too hot then there is cracking noises, and radiators get hot, before cooling down again.
Spent last two days trying to balance the rads and thought I had succeeded yesterday. Problem back again this morning.
I have tried opening fully all the lockshield valves then once heat is at the rads, I have started at No1 rad (nearest to pump) turning it right down then opening slightly; moving to nos. 2, 3, 4 and 5. and doing the same, opening each subsequent rad slightly more. No. 5 lockshield fully open.
Even tried closing down all lockshields, hoping to get water and air just flowing through the pipes,allowing air to escape (Honeywell Auto Air Vent fitted). After that I started at No 5 radiator, then worked backwards. Again that seemed to work until this morning. Hot water to taps is OK.
Any suggestions as to what I can do, or am I doing something wrong ?

 

[entirelyuseless]

I have finally restored the central heating to normal. One important fact I learned yesterday is that before attempting to remove an airlock in the pipes, allow the water to cool right down. I had been attemtping to remove the air and balance the radiators whilst the water was still HOT.
After allowing the water to cool right down, I then tackled each radiator in turn starting at No.5, then working backwards.