"Bought this to replace a standard thermostat. The time clock was built into our combination boiler and therefore we were forever switching to constant and then forgetting to switch it back, then waking at three in the morning sweltering. This has six programmable time slots, each with their own temperature. If you want it hottter or cooler right now you just push a button to select the temerature you want. It then switches back at the next timed event. It is easy to install and works brilliantly. It will save us a fortune. Looks good as well, it is small and neat. Instruction leaflet could be better but hey."