What to do when your boiler wont turn on in London? Cold house, no heating, no hot water. A boiler that refuses to start can point to pressure drops, faulty thermostats, ignition faults, frozen condensate pipes or issues with the main power supply. People dealing with boilers that stop working usually want quick checks they can try before calling someone. Low pressure, tripped switches, blocked flues and flashing fault codes are the most common early signs. These things can stop the boiler from