Programmer or timer not turning heating on
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Most likely cause & what to check
The central heating programmer (timer) controls when the heating and hot water operate. If the heating is not coming on at programmed times, work through the following checks before assuming a boiler fault.
Check the programmer clock — it may have reset to 00:00 after a power cut. The programmed on/off times will be lost. Reprogram the current time and your heating schedules. Many older mechanical timers lose their settings after even a brief power interruption.
Check the mode — most programmers have three modes: OFF, TIMED (runs to schedule), and ON (continuous). Confirm it is set to TIMED and that the heating schedule has at least one on-period set.
Check the thermostat — even if the programmer is calling, the boiler will not fire if the room thermostat is set below the current room temperature. Turn the thermostat above room temperature and listen for the boiler to fire.
Check the manual override on the programmer — most allow you to press a button to turn heating on manually, regardless of the timer. If this fires the boiler, the programmer itself works but the schedule is incorrectly set.
If the programmer is genuinely faulty: a direct replacement is straightforward — they plug into a standard 3 or 4-wire backplate. Popular UK brands (Honeywell, Drayton, Potterton) are widely available for £20–£60. Photograph the wiring connections before removing the old unit to ensure correct reconnection.
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Frequently asked questions
My heating won't turn off — could this be the programmer?
Yes — if the programmer relay is stuck in the "on" position, the boiler will fire continuously regardless of the time or room thermostat. Test by turning the room thermostat to its lowest setting — if heating continues, the fault is in the programmer or wiring, not the thermostat. A replacement programmer costs £20–£100 depending on type.
Will a smart thermostat fix programmer problems?
Often yes — replacing an old mechanical programmer with a smart thermostat (Hive, Nest, Drayton Wiser) gives you reliable scheduling, remote control, and better integration with your boiler. Installation costs £150–£300 including the thermostat unit and a Gas Safe engineer fitting it correctly.
My programmer shows the correct time but heating still doesn't work — what's wrong?
Check the programme is set to "Auto" or "Timed" mode rather than "Off" or "Constant." Many programmers have a mode button that cycles through options — it is easy to accidentally set it to "Off" permanently. Also confirm the room thermostat is set above the current room temperature.