8 key boiler checks every homeowner should complete before winter arrives

Make sure your heating system is working properly before the cold weather begins

If your heating has been off for months, the last thing you want is to find out the boiler has a fault when the first cold spell arrives. In many homes, problems only become obvious once the temperature drops and the central heating is suddenly needed again.

The reassuring part is that you do not need to be a heating specialist to do some basic checks. Running the boiler, reviewing the pressure and making sure the radiators heat up properly can help you spot trouble early, before it turns into a more expensive repair.

Below, we explain how to tell whether your boiler is winter-ready, what you can safely check yourself and when a professional should step in.

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Eight key boiler checks before winter

1. Switch on the heating and confirm it runs

The easiest way to see whether your boiler is ready is to test it before you actually need it. Start by checking that the boiler is turned on and, if it has a summer or hot-water-only setting, change it to central-heating mode.

Then raise the room thermostat a few degrees above the current temperature. That should signal the system to start heating the house. Let it run for about 20 to 30 minutes, then check whether the radiators are beginning to warm up.

If nothing happens, look at the programmer or timer. The boiler may be fine but simply not set to come on. If it still will not start even though the controls appear to be correct, check for warning lights or error codes before doing anything else.

2. Inspect the boiler pressure

Low pressure is one of the most common reasons a central heating system stops working properly. Fortunately, it is usually easy to check. Most modern boilers have a pressure gauge on the front or underside of the unit, while some newer models display the reading digitally.

For many sealed systems, the pressure should be between 1 and 1.5 bar when the heating is cold. However, the correct range varies from one boiler to another, so always refer to the manufacturer’s instructions.

If the pressure is too low, the boiler may need repressurising. On some systems, this means opening a filling loop beneath the boiler so more water can enter the heating circuit.

The exact method depends on the model, so follow the instructions carefully and only do this when the system is switched off and cool. If you are not sure, call a heating engineer.

Keep checking the pressure afterwards. If it keeps dropping, there may be a leak or another fault that needs professional attention. Excessively high pressure should also be investigated.

3. Examine the radiators and bleed them if needed

After the heating has been on for a while, check that every radiator is warming up. If the top is cold but the bottom is warm, air may be trapped inside and preventing hot water from circulating properly. That can usually be fixed by bleeding the radiator.

Here is how to do it:

1. Turn off the central heating and let the radiator cool down
2. Place a cloth or small container under the bleed valve, usually located at the top of the radiator
3. Insert a radiator key and slowly turn the valve anticlockwise
4. You should hear a hissing noise as the trapped air escapes
5. When water starts to come out, close the valve carefully without overtightening it
6. Check the boiler pressure afterwards, because bleeding radiators can lower it

If a radiator is cold at the bottom, that may point to sludge build-up or another circulation issue. If one radiator stays completely cold, make sure its valves are open before calling an engineer.

4. Review the thermostat and heating controls

Heating controls can be easy to forget about, especially if they have not been used since the warmer months. Check that the thermostat is working and that the schedule still matches your routine. If you have a smart thermostat, make sure it is connected and that any programmed settings are correct.

Ian Palmer-Smith, appliance repair expert at Domestic & General, says unexpected heating behaviour can sometimes have a simple explanation. “If you're noticing your boiler is turning on or off sporadically throughout the day, you may need to simply adjust your timer settings using your boiler manual for help.”

It is also worth checking the thermostatic radiator valves on individual radiators, as these may have been turned down or switched off during the warmer months.

Remember that if the room is already warmer than the thermostat setting, the heating will not come on. That is normal and does not necessarily mean the boiler is faulty.

For more information on heating settings, see our guide to the ideal temperature for every room in your home.

5. Look for leaks and listen for odd noises

While the heating is running, take a few minutes to inspect the boiler, visible pipework and radiators for signs of trouble.

Look for water dripping from pipes or valves, damp patches beneath radiators and visible corrosion. Even a small leak can cause the system pressure to fall over time, so it is worth getting checked before the issue gets worse.

Listen to the boiler as well. Some noise during normal operation is expected, but repeated banging, whistling or gurgling can point to trapped air, circulation problems or another fault.

Unusual noises are not always serious, but if they are new or becoming louder, it is sensible to have the system examined by a qualified heating engineer.

6. Inspect the condensate pipe

If you have a modern condensing boiler, it will have a condensate pipe that carries away waste water produced during operation. In some homes, part of this plastic pipe runs outside, and in prolonged freezing weather the water inside can freeze and stop the boiler from working.

Before winter arrives, check whether any accessible outside sections are insulated properly and make sure the pipe outlet is not visibly blocked.

If the boiler stops working in freezing conditions, a frozen condensate pipe could be the reason, especially if the boiler is making gurgling noises or showing an error code. Palmer-Smith recommends gently warming the frozen section by applying a hot water bottle directly to the pipe.

You can also use warm water, but never boiling water, which could damage the plastic. Only do this if the pipe is safely reachable from ground level, and do not use a naked flame.

Worcester Bosch, for example, says that once the pipe has thawed, you may need to reset the boiler according to its instructions. If the issue continues, contact a heating engineer.

7. Test the carbon monoxide alarm

Every home with a gas boiler should have a working carbon monoxide alarm. Carbon monoxide is a poisonous gas that cannot be seen, smelled or tasted, and it can be produced when gas appliances such as boilers do not burn fuel properly.

Press the test button on the alarm, following the manufacturer’s instructions, and check that it has not passed its replacement date. If the unit uses a replaceable battery, make sure that is still working too.

A carbon monoxide alarm is an essential safeguard, but it is not a replacement for regular boiler servicing. If the alarm sounds, leave the property immediately, get into fresh air and seek emergency help. Do not ignore the warning or assume the alarm is defective.

8. Check when the boiler was last serviced

Even if the boiler seems to be working perfectly, it is worth checking when it was last professionally serviced. An annual service can help detect developing faults and confirm that the appliance is operating safely. “Having your boiler serviced annually is a great action to take to prevent boiler breakdowns, as well as improve its efficiency,” says Palmer-Smith.

Servicing may also be required to keep the manufacturer’s warranty valid. If the boiler has not been serviced within the past 12 months, now is a good time to arrange an appointment before engineers become busier. Gas boilers should always be serviced by a Gas Safe registered engineer.

If the boiler is older and keeps developing faults, it may also be worth considering whether repairs are still cost-effective. Our guide to how much a new boiler costs in the UK explains what to expect if replacement becomes necessary.

When should you call a Gas Safe engineer?

Homeowners can handle basic checks, but some problems should always be left to professionals.

Call a Gas Safe registered engineer if your boiler repeatedly loses pressure, develops ongoing faults, leaks, makes unusual noises or stops working after basic troubleshooting. Never remove the boiler casing or try to repair gas components yourself.

If you smell gas or think there may be a leak, do not use electrical switches, smoke or create any naked flame. Open doors and windows if it is safe, leave the property and call the National Gas Emergency Service on 0800 111 999 once you are in a safe place.

In the end, checking your boiler before winter is about finding problems while there is still time to deal with them. A few minutes spent testing the system now could spare you from discovering a fault on the coldest day of the year.

Once you know everything is working, you can then focus on cutting running costs. Our guide to energy-saving tips for your home explains how to keep bills down during the colder months.