Hello. Boiler is a Worcester Greenstar heatslave 12/18 (oil )running hot water and 6 radiators. Serviced early this year, and has not had any issues, until now. Hot water is working but heating is not .Room stat is OK, when I turn it up and down there is a clicking on ad off in the boiler cabinet . The pressure is within normal range, all radiators have been bled and the boiler will sometimes run for about 2 minutes and then switch off.No heat comes through to the rads. The lockout indicator light does not come on. This has happened suddenly, it was working fine up until yesterday. Any advice much appreciated. PS of course, being today, every heating bloke has the phone switched off! And why not?