How do I turn my central heating on?

Make sure the boiler has power, set the timer or programmer to on or to a timed period that is active now, and turn the room thermostat above the current room temperature. Open the radiator valves in the rooms you want heated.

What do the pins on a heating timer mean?

Each pin or tab usually covers 15 minutes. Pins pushed in, or down on some models, are on periods. Pins left out are off. The exact direction is shown on the dial or in the instructions.

Why does my heating come on at the wrong time?

The timer's clock is usually wrong, often after a power cut or the clocks changing. Reset the time first. If it keeps drifting, the timer may need replacing.

What is the difference between CH and HW on a programmer?

CH is central heating and HW is hot water. Two-channel programmers control them separately, so a hot water cylinder can heat at different times from the radiators.

Should the heating timer be set to on or auto?

Auto, timed or the clock symbol, so it follows your schedule. On runs the heating constantly, controlled only by the thermostat, which usually costs more.

Radiators and heating guides →

How to set a central heating timer or programmer

To set a central heating timer, first set the clock to the correct time, then choose when the heating should come on and go off, and finally put the timer into its automatic or timed mode so it follows that schedule. On a mechanical dial you do this by turning the dial to the current time and pushing in or pulling out the small segments for the periods you want heat. On a digital programmer you use the set, program or menu button to enter on and off times for each day. The timer only decides when the heating may run. The room thermostat still decides how warm it gets, so if the timer says on and nothing happens, check the thermostat is set above the room temperature.

Loyal Plumbers · Updated 27 September 2026

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Work out which type of timer you have

Heating timers fall into a few types. Most sit on the front of the boiler, on the wall near the boiler or next to the hot water cylinder, and the model name is usually printed on the front or under a flap.

Common types of heating timer and programmer
Type	How to recognise it	What it controls
Mechanical dial timer	A round 24-hour dial with small tabs or pins around the edge and a switch marked timed, on or off	Usually heating only, often built into a combi boiler
Single-channel digital programmer	A small screen with buttons such as set, program, advance and boost	Heating only, common with combi boilers
Two-channel programmer	Separate settings or buttons for CH (central heating) and HW (hot water)	Heating and a stored hot water cylinder, each on its own schedule
Programmable room thermostat	A thermostat on the wall with a clock and schedule built in	Both the timing and the temperature of the heating
Smart thermostat	Controlled through an app as well as the wall unit	Timing, temperature and sometimes hot water, depending on the system

How to set a mechanical dial timer

Dial timers are simple once you know what the tabs mean. Each tab usually covers 15 minutes. Tabs pushed in or down, depending on the model, are on; tabs left out are off.

Set the clock by turning the outer dial clockwise until the current time lines up with the arrow or marker. Do not turn it anticlockwise unless the instructions say you can.
Push in the tabs for the periods you want the heating on, for example 6.30 to 8.00 in the morning and 17.00 to 22.30 in the evening. Leave the rest out.
Set the selector switch to timed, auto or the clock symbol. On or constant overrides the schedule and runs all the time; off stops it completely.
Check the time again the next day. If the dial is drifting or stopped, the timer may have failed or lost power.

How to set a digital programmer

The buttons differ between makes, but most digital programmers follow the same order. If you can find the model number, the manufacturer's instructions are usually available online and will show the exact buttons.

Set the day and time first. This is usually done by holding the set, clock or menu button, then using the plus and minus or arrow buttons.
Choose how the programme repeats. A 24-hour programmer uses the same times every day, a 5/2-day programmer has one schedule for weekdays and one for weekends, and a 7-day programmer lets you set each day separately.
Enter the on and off times for each period, often called ON1, OFF1, ON2 and OFF2. Save or confirm each one.
On a two-channel programmer, repeat this for the hot water channel. Most homes need the cylinder heated for an hour or two before the main times people shower or bath, not all day.
Put each channel into auto or timed mode. Many programmers also offer once, where the schedule applies for one period only, and always on or always off.
Use advance to jump forward to the next programmed period, and boost to add an extra hour or so of heat without changing the schedule.

If the screen is blank or the time resets after a power cut, the programmer may have a backup battery that needs replacing, or it may be failing. Check the manual before replacing parts, and never open a unit wired to the mains yourself.

Timer, thermostat and radiator valves: who does what

Much of the confusion about heating controls comes from expecting one control to do another's job.

The timer or programmer only switches the heating on and off at set times. The room thermostat measures the air temperature and tells the boiler to stop once the room reaches its setting, even while the timer still says on. Thermostatic radiator valves then fine-tune individual rooms, so a bedroom can stay cooler than the living room.

For the heating to run, all three have to agree: the timer must be in an on period, the thermostat must be set above the room temperature, and the radiator valves must be open. If any one of them says no, the radiators stay cold.

A schedule that works for most homes

Start with heat for about half an hour before you get up and before you get home, and switch it off shortly before you leave and before bed. The house holds its warmth for a while after the boiler stops. Adjust the times by 15 minutes at a time until the rooms are warm when you need them.

Our guide on when to turn the heating on explains why a timed schedule usually costs less than leaving the heating on low all day, and what temperature to set the thermostat to.

Do not forget the clock change

The clocks go back at 2am on Sunday 25 October 2026. Most smart thermostats and many newer programmers update themselves, but mechanical dials and many older digital units do not. If yours is one of those, move it back an hour that weekend, or the heating will come on an hour early all winter.

When the timer is set but the heating still will not come on

If the display shows an on period and the thermostat is turned up but the radiators stay cold, the problem is usually somewhere else.

Check the boiler has power and is not showing a fault code or low pressure.
Look for a separate thermostat that might be set low, or a wireless thermostat with flat batteries.
On systems with a cylinder, a stuck motorised zone valve can stop the heating while the hot water still works.
After a power cut, the programmer may have lost its settings or its clock. See our guide on heating controls after a power cut.
If you have hot water but no heating, work through our guide to that fault before assuming the timer is to blame.

Replacing or upgrading a heating timer

Programmers and wall thermostats are wired into the boiler or wiring centre, and often into the valves of a cylinder system. Replacing one means isolating the electrical supply and matching the new unit to the existing wiring, so it is a job for a heating engineer rather than a quick swap.

If your controls are old, hard to read or do not suit how you use the house, it can be worth upgrading rather than replacing like for like. Our guide on upgrading heating controls explains what to ask for. For faults, Loyal Plumbers covers London and everywhere inside the M25 with 10 vans, 24 hours a day. Our call-out charge is £60.

Common questions

How do I turn my central heating on?: Make sure the boiler has power, set the timer or programmer to on or to a timed period that is active now, and turn the room thermostat above the current room temperature. Open the radiator valves in the rooms you want heated.
What do the pins on a heating timer mean?: Each pin or tab usually covers 15 minutes. Pins pushed in, or down on some models, are on periods. Pins left out are off. The exact direction is shown on the dial or in the instructions.
Why does my heating come on at the wrong time?: The timer's clock is usually wrong, often after a power cut or the clocks changing. Reset the time first. If it keeps drifting, the timer may need replacing.
What is the difference between CH and HW on a programmer?: CH is central heating and HW is hot water. Two-channel programmers control them separately, so a hot water cylinder can heat at different times from the radiators.
Should the heating timer be set to on or auto?: Auto, timed or the clock symbol, so it follows your schedule. On runs the heating constantly, controlled only by the thermostat, which usually costs more.

Sources and further reading

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