Worcester-Bosch Greenstar 24 Ri boiler won't turn off !?

Intermittently the boiler stays on all night. The set point is 14 but the temp is 23. No flame showing on the wireless stat. and the new programmer timer is saying off at 3 in the morning but the boiler is blazing away. have to turn it off with the boiler stat.
Any ideas? Could it be the boiler which is under guarantee?