My wall mounted Glow Worm 40 -50 did the same on Friday 19th Feb. Called an engineer. He said a thermostat had "popped out". (Maybe a solenoid?) He pointed to the right side of the bottom of the boiler . (I had removed to cover that covers the piezo electric button and thermostat control knob. He just pushed it back in and all is now ok.
Pete, February 2010