When to turn the heating on, and is leaving it on low cheaper?
There is no set date to turn the heating on in the UK. The practical rule is to switch it on when the rooms you use regularly drop below about 18°C, which the NHS gives as the minimum to aim for, especially for anyone older, very young or unwell. For most London homes that happens somewhere between late September and the end of October. When it does, a timed schedule that heats the house when you are in and awake almost always costs less than leaving the heating on low all day. Before the first cold snap, run the heating once for half an hour to check for cold radiators, noises or a pressure drop, so any fault is found before engineers are at their busiest.
Loyal Plumbers · Updated
Discuss your plumbing workGo by the temperature, not the calendar
People argue about whether the heating should go on in October or wait until the clocks change, but what matters is how warm the rooms actually are. A cheap thermometer, or the reading on a room thermostat, is more reliable than how the weather looks outside.
The NHS advises heating the rooms you use to at least 18°C in cold weather. Lower temperatures matter more for some people than others: babies, anyone over 65, and people with heart or lung conditions are more affected by cold homes. If someone in your household falls into one of those groups, do not hold off to save a few days of gas.
| Room | Starting point | Notes |
|---|---|---|
| Living room and rooms used during the day | 18°C or a little above | The NHS minimum for cold weather; most people are comfortable around 18 to 21°C |
| Bedrooms | Around 18°C | Cooler at night suits many people, but do not let rooms used by vulnerable people fall below 18°C |
| Hallways and spare rooms | Lower, with the door closed | Keep radiators on low rather than off if there is damp or condensation |
| Rooms with exposed pipes or an empty flat | Frost protection at minimum | Stops pipes freezing when nobody is there |
Is it cheaper to leave the heating on low all day?
For a typical gas boiler and radiator system, no. A house loses heat all the time it is warmer than outside, and it loses it faster the warmer it is. Keeping it warm through the hours when nobody is home or everyone is asleep means paying to replace that lost heat for longer. The Energy Saving Trust says heating the home only when you need it, with a timer, is the cheaper approach.
There are a few exceptions worth knowing about.
- Heat pumps work best running steadily at a low flow temperature for long periods, so the advice for them is different. Follow your installer's settings.
- Homes with damp or condensation problems may do better with a low, steady background heat in cold rooms than with long cold gaps.
- Homes with very heavy walls can take a long time to warm up. Bringing the heating on a little earlier usually works better than leaving it on all day.
- If someone is at home all day, especially someone vulnerable, heat the rooms they use for as long as they are in them.
How to set up a sensible schedule
Most savings come from getting the timer and thermostat to do their separate jobs. The timer or programmer decides when the heating is allowed to run. The room thermostat decides how warm it gets. Radiator valves fine-tune individual rooms.
- Set the heating to come on about 30 minutes before you get up and switch off shortly before you leave.
- Set it to come on about 30 minutes before you get home and switch off shortly before bed. The house stays warm for a while after.
- Set the room thermostat to the lowest temperature you are comfortable at, usually somewhere between 18 and 21°C. Every degree you turn it down saves gas.
- Turn thermostatic radiator valves down in rooms you do not use much, rather than switching the whole system on and off.
The clocks go back at 2am on Sunday 25 October 2026. Many mechanical and older digital timers do not change automatically, so check yours that weekend or the heating will come on an hour out.
Checks to do the first time you switch on
A boiler that has only been heating water for five months can show faults the moment the radiators are asked to work. Running the heating on a mild day in late September or early October gives you time to sort anything out before the first cold spell.
- Put the heating on and wait 20 to 30 minutes, then feel every radiator. Cold at the top usually means trapped air; cold at the bottom usually means sludge.
- Bleed any radiator that is cold at the top, then check the boiler pressure gauge. On most sealed systems it should read about 1 to 1.5 bar when cold. Top it up if it has dropped.
- Listen for banging, kettling or gurgling from the boiler and pipes.
- Check the boiler display for fault codes, and look under it and around radiator valves for drips.
- Test your carbon monoxide alarm. If you do not have one in rooms with a gas appliance, fit one.
- If your boiler is older and has a pilot light that you turned off for the summer, relight it following the instructions and check that the flame is blue.
Book the service before the rush
An annual service is the best way to avoid a breakdown in the first cold week, when everyone switches on at once and faults that were hidden over summer show up. Booking it in September or October means the engineer sees the boiler working hard on the heating, not just the hot water.
If you are a landlord, the gas safety check can often be done on the same visit, so tenants go into winter with a boiler that has been checked and a current record.
If the heating will not come on
If you switch on and nothing happens, check the simple things first: that the timer is set to on or an active period, the room thermostat is turned up above room temperature, the boiler has power, and the pressure is not below 1 bar. Our guides to a boiler that is not working and to hot water but no heating walk through the rest.
If radiators stay cold, the boiler shows a fault, or the pressure keeps dropping, Loyal Plumbers can help. We run 10 vans across London and everywhere inside the M25, 24 hours a day, with Gas Safe registered engineers for gas work. Our call-out charge is £60.
Common questions
- What month should you turn the heating on in the UK?
- There is no official month. Most households switch on between late September and the end of October, when indoor temperatures start falling below about 18°C. Go by the room temperature, not the date.
- What temperature should my house be in winter?
- The NHS advises heating the rooms you use to at least 18°C in cold weather. Many people are comfortable between 18 and 21°C. Set the thermostat to the lowest temperature you find comfortable.
- Is it cheaper to leave the heating on low all day?
- Usually not with a gas boiler and radiators. The house loses heat for longer, so you pay to replace it for longer. Heating on a timer when you need it is normally cheaper. Heat pumps are the exception.
- Should I bleed my radiators before turning the heating on?
- Bleed any radiator that is cold at the top once the heating has run for a while. Then check the boiler pressure, as bleeding lets water out and can drop it below 1 bar.
- Should I leave the heating on while I am away in winter?
- Leave it on a low or frost-protection setting rather than fully off, so the pipes do not freeze. For longer absences in an empty property, get advice on draining down or protecting exposed pipework.
Sources and further reading
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