How can I fix my Potterton Profile 40e boiler?

The hot water side of the central heating system works fine.But no heating,the hall thermostat works,when operating the programmer,the boiler should come on straight away when switching to continuous but it does not.But it does when switching to hot water.the programmer is ok as I have changed it and the pump seems to be work on hot water. Are there any fuses on the boiler PCB .