I too have a problem with my Potterton Suprima 50L, but unlike those listed by BBC Watchdog viewers, mine won;t switch off! The controller time setting may be comanding OFF, the roomstat may be set low, the central heating switch may be OFF, even the controller itself may be OFF, yet I can come in from work and find the house stifflingly hot, with the boiler and pump running continuously, effectively throwing £20 notes out of the flue. The only thing that works is switching the boiler off at the mains. Does anyone have any ideas?