Worcester Bosch Greenstar 30 CDi boiler supporting the central heating after being off all summer.

Hot water is fine.

Central heating starts up, boiler fires up etc., temperature starts to climb up into 70's, but then boiler flame goes out and temperature drops right back down again, reaches low 40's and starts up again. Follows same cycle continuously but no heat getting through to radiators at all.

Geoff, October 2011

My mother has exactly the same issue on the same model of boiler. I replaced the diverter valve and motor yesterday but it has made no difference. Essentially the pump doesn't come on to circulate the water so the temperature goes mad and the boiler switches off until such time (long time) that the temperature goes back down. A reset usually gets it working again (for a while). Still investigating our problem.....

Andy., November 2011