Help, I have a CSI 85A which when you call for central heating fires up for around 6 seconds then goes out then fires up again then goes out.....and so on. Run the hot water and it fires up fine, no problems at all, turn off the tap and the CH keeps going. Ive changed the electrodes and cables, same problem. Has anyone got an idea what it might be ?, thanks

Graeme, May 2010