No heating? What to check before you call someone

A cold house is stressful, but many no heating call-outs turn out to be a setting, a power cut or a frozen pipe outside. The checks below are all safe for anyone to do. None of them involve opening the boiler or touching any gas parts.

Safety: If you smell gas, or think there could be carbon monoxide, don't try any of these checks. Turn off the gas at the meter if you can, open doors and windows, get everyone out into fresh air and call the National Gas Emergency Service on 0800 111 999. Don't use light switches or anything that could make a spark.

Does the boiler have power?

Start with the simplest thing. Look at the boiler's display or lights. If they're blank:

• Check other lights and sockets work, in case there's a power cut.
• Check the switch or fused spur next to the boiler is on.
• Look at your consumer unit. If a breaker or RCD has tripped, switch it back on once. If it trips again straight away, leave it off and call a registered electrician.

If there's water dripping near the boiler or its wiring, keep away from any wet electrics and don't reset anything until it's been looked at.

Is the thermostat or timer stopping the heating?

The boiler only heats your radiators when the controls ask it to. Check that:

• The heating isn't switched off or set to a summer or hot water only mode on the boiler or programmer.
• The room thermostat is set above the current room temperature. Turning it up to about 20°C is a good test.
• The timer or programmer shows the right time. After a power cut, clocks often reset and the heating can switch on at the wrong times.
• A wireless or battery thermostat has working batteries and is talking to its receiver. A blank screen usually means flat batteries.
• The radiators themselves are turned on. Radiator valves are often turned down over the summer and forgotten.

What should the boiler pressure be?

Most combi and system boilers have a pressure gauge on the front. Manufacturers and Citizens Advice say it should usually read between 1 and 1.5 bar. If it has dropped below 1 bar, that alone can stop the boiler working.

Many manufacturers let you top the pressure up yourself using the filling loop, following the steps in your boiler's manual. If you're not sure how, or the pressure keeps dropping after you top it up, there may be a leak and it's a job for an engineer. Our guide to a boiler losing pressure explains this in more detail.

Could a frozen condensate pipe be the problem?

Modern condensing boilers get rid of waste water through a plastic pipe, often white, that runs outside to a drain. In freezing weather this water can freeze and block the pipe, which makes the boiler stop. Worcester Bosch says you may hear gurgling from the boiler and see a fault code on the display.

1. Find the plastic condensate pipe where it leaves the boiler and runs outside.
2. Pour warm water slowly along the outside section of the pipe, especially at bends and the open end. Use warm water, not boiling, which can damage the plastic.
3. Once it's thawed, reset the boiler as your manual describes.

Only thaw the outside plastic pipe. Never open the boiler casing or pour water on the boiler itself. If the pipe keeps freezing, ask an engineer about insulating it or changing how it's run.

Is gas getting to the boiler?

If you have a gas hob or fire, see whether it lights normally. If nothing gas works, check:

• A prepayment meter has credit and hasn't run into emergency credit.
• Whether your neighbours have a problem too, which could point to a supply fault in the area.
• That nobody has turned the gas off at the meter, for example during building work.

If other gas appliances work but the boiler won't light, the fault is in the boiler. Don't try to fix it yourself.

How do I reset my boiler?

Most boilers have a reset button or a reset option on the display. Look up any fault code in your manual first, because it often tells you what the problem is and whether a reset is safe. Then reset once, as the manual says, and give the boiler a few minutes to restart.

If it locks out again, stop there. Pressing reset over and over won't fix the cause and can hide a fault that needs an engineer.

No heating but hot water working?

If your taps run hot but the radiators stay cold, the boiler is lighting, so the problem is usually in the heating side. Start with the controls: the heating may be off, the thermostat set too low, or the timer in the wrong period. If the controls are right, the cause is often a part such as the diverter valve or the pump. These need an engineer to diagnose.

If only some radiators are cold, or they're cold at the top, try bleeding them. That's a separate job you can do safely, covered in our guide to bleeding a radiator.

When to call a Gas Safe registered engineer

If you've done these checks and still have no heating, it's time for a professional. Anything inside the boiler, the gas supply or the flue must be left to a Gas Safe registered engineer. It's against the law for anyone else to do gas work. Call one if:

• The boiler keeps locking out or showing a fault code after one reset.
• The pressure keeps dropping, or water is leaking from the boiler or its pipes.
• You hear new banging, whistling or grinding noises.
• You see soot, scorch marks or a yellow or orange flame instead of a blue one.

When the engineer arrives, ask to see their Gas Safe ID card. Check the photo matches the person, the card is in date and the back lists the type of gas work they can do, such as domestic boilers.

If you rent, tell your landlord straight away rather than calling an engineer yourself. If you own your home, check whether a boiler warranty, home emergency cover or insurance policy covers the repair before you book.