Heating won't come on after the summer? What to check first

If your heating won't come on now the weather has turned, the cause is often simple. After months switched off, a timer that has slipped, a thermostat with flat batteries, low boiler pressure or a radiator valve that has stuck are the usual culprits, and you can check most of them yourself in a few minutes.

This post walks through those checks in a sensible order, then explains which signs mean it's time for a heating engineer. You can safely look at the controls, the boiler display and the pressure gauge, but never remove the boiler casing or touch any gas parts. Those are jobs for a Gas Safe registered engineer only.

Start with the thermostat and the timer

Most "broken" heating at the start of autumn turns out to be the controls. Check these first:

• The programmer or timer. Many are set to "hot water only" over the summer. Make sure the heating channel is switched on or set to a timed programme, and that the clock shows the right time.
• The room thermostat. Turn it up a few degrees above the room temperature. If it's a wireless or battery-powered thermostat, a blank or dim screen usually means the batteries need changing.
• Smart controls. If you use an app, check it hasn't stayed in a holiday or "away" mode since the summer.

The clocks go back on Sunday 25 October 2026. Older timers don't change on their own, so if your heating seems to come on an hour early or late afterwards, the clock on the programmer is the first thing to check.

Check the boiler has power and pressure

Next, look at the boiler itself, from the outside only. If the display is blank, check the fused switch next to the boiler (often called a fused spur, a wall switch with a small fuse in it) is on, and that nothing has tripped at your consumer unit, the box of switches that controls your home's electrics.

If the display is on, check the pressure gauge. On most combi and system boilers it should read roughly 1 to 1.5 bar when the heating is cold, though your boiler's manual gives the exact figure. Pressure often drops a little over the summer, and many boilers won't fire if it falls too low. Our guide on how to top up boiler pressure shows you how to bring it back up safely.

If you top it up and it drops again within days, that points to a leak or a fault somewhere in the system, and our post on why a boiler keeps losing pressure explains the likely causes.

Look for a fault code

If the boiler shows a code or a warning light, write it down before you do anything else. The manual will tell you what it means, and some codes simply ask you to press reset. It's fine to reset the boiler once. If it locks out again, stop there, because repeated resets can hide a fault that needs looking at. If you have a Vaillant, our guide to Vaillant boiler fault codes covers the common ones.

When the boiler fires but radiators stay cold

Sometimes the boiler lights and the pipes near it get warm, but some or all of the radiators stay cold. After a long summer off, three things are worth knowing about:

1. Stuck radiator valves. A thermostatic radiator valve, or TRV, is the numbered dial on the side of a radiator. The small pin inside it can stick when it hasn't moved for months. Turning the dial fully down and fully up a few times often frees it.
2. Trapped air. A radiator that's warm at the bottom but cold at the top usually needs bleeding. Our step-by-step guide to bleeding a radiator shows you how.
3. A sticking pump. The pump pushes hot water round your radiators. If it has sat still all summer it can seize, and you may hear the boiler run while the radiators stay cold. This one needs an engineer.

A radiator that's cold at the bottom but warm at the top is a different problem, usually sludge, and won't be fixed by bleeding.

Signs it's a job for an engineer

Stop checking and book a heating engineer if:

• the boiler keeps locking out after one reset
• the pressure keeps dropping, or you can see water dripping from the boiler or pipework
• you hear banging, gurgling or a loud humming from the boiler or pump
• the boiler fires but none of the radiators warm up
• the controls are working but the boiler doesn't respond at all

If you smell gas, don't use the boiler or any switches. Open windows, turn off the gas at the meter if you can, leave the property and call the National Gas Emergency Service on 0800 111 999.

How we approach a heating repair

When we come out to a heating system that won't start, we don't stop at the obvious symptom. We look over the whole system to find what's actually causing the problem, explain what we've found in plain terms, and give you the price for any repair before we start work. We work on all makes of boiler and heating system, whoever fitted them. You can read more on our central heating repair page.

Avoiding a cold start next autumn

A few habits make it far less likely you'll be left without heating on the first cold evening:

• Run the heating for 15 minutes or so once a month over the summer, so the pump and valves keep moving. Some modern boilers do this automatically.
• Turn your heating on for a test run in September, before you really need it.
• Have the boiler serviced every year, ideally before winter, so small faults are found early.

Our boiler servicing page explains what a service includes.

If you've worked through these checks and your heating still won't come on, Parks Plumbing & Heating can help. Book a central heating repair visit through our central heating repair page and we'll find the cause and get your home warm again.

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