Your Diverter Value has probably got a split diaphram. You can buy service kits for about £20 or a new DV will cost about £90. You will need a plumber or heating engineer to replace it. It should take longer than 1.5 hours to do.
To check if it's your DV, ensure your pressure is at least 1 bar, then try to operate the microswitch attached to the DV with a screw driver. If your CH should then come on.
NickA, March 2007
