Greenstar 30 CDi central heating not working?

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