Glowworm 330+ boiler starts up at night?

The boiler starts up at night despite both system controls being set to off and it not being cold enough for the system safety thermostat to operate, if I pressed the reset button it shut down, but restarted some time later: if I turned off the power the system reverted to correct operation for a while. I first noticed that during the daytime the boiler was running constantly despite the Room tmeperature being above the CH thermostat setting.