What to do when your boiler breaks down in winter

If your boiler stops working on a cold day, check first that nothing is unsafe, then work through a few simple checks before you book a repair. Many winter breakdowns come down to something small, such as a frozen pipe outside, low pressure or a timer that has lost its settings, and some of these you can put right yourself.

This post covers what to do straight away, the checks you can safely make, how to keep warm while you wait and when it's time for a Gas Safe registered engineer. You can look at the display, the pressure gauge and the controls, but never remove the boiler's casing or try to repair anything inside it.

If you smell gas, do this first

If you can smell gas, or think there might be a leak, deal with that before anything else.

• Open doors and windows to let fresh air in.

• Turn off the gas at the meter if you can reach it safely, and turn off any gas appliances.

• Don't use light switches or other electrical switches, and don't smoke or light a flame.

• Call the National Gas Emergency Service on 0800 111 999, free and open 24 hours a day.

Carbon monoxide needs the same care. It's a poisonous gas you can't see or smell, given off when a gas appliance isn't burning properly. Headaches, dizziness, feeling sick and tiredness are common early signs, and they're easy to mistake for flu. If your carbon monoxide alarm goes off, or people feel unwell indoors and better outside, turn off the boiler, get everyone into fresh air, call the same number and get medical advice.

The emergency service makes the gas supply safe. It doesn't repair your boiler, so leave it switched off until a Gas Safe registered engineer has found and fixed the fault.

Why boilers break down more in cold weather

In winter your boiler runs for longer and works harder, so small faults that went unnoticed in the summer start to show.

Most modern gas boilers are condensing boilers. They recover extra heat from the exhaust gases, which produces water called condensate. A plastic pipe carries it away to a drain, and where that pipe runs outside it can freeze in a cold snap. The ice blocks the pipe and the boiler shuts itself down to stay safe.

Safe checks you can make at home

None of these involve opening the boiler.

1. Read the display. Most boilers show a fault code when they stop. Write it down, along with the make and model on the front. Our guide to boiler fault codes explains what the common ones point to.

2. Check the power and controls. Make sure the boiler's switched fused spur (the wall switch next to it) is on and nothing has tripped at the fuse box. A power cut can reset the timer, and a wireless thermostat may just need new batteries. Turn the thermostat up a few degrees above the room temperature to see if the boiler fires.

3. Check the pressure gauge. On many boilers it should read around 1 to 1.5 bar when the heating is cold, but check your manual for yours. If it's below 1 bar the boiler may lock out. You can top it up through the filling loop if your manual shows how, but if the pressure keeps falling there's a leak to find. Our post on boiler pressure that keeps dropping goes through this in more detail.

4. Look at the condensate pipe outside. If it's frozen, thaw it with warm water from a watering can or a hot water bottle, never boiling water. Our guide to a frozen condensate pipe shows how to do it safely.

5. Reset it once. When you've put something right, press the reset button once, as your manual describes. If the boiler locks out again, leave it switched off and book a repair.

What you should never do

• Never remove the boiler's casing. Behind it are gas parts and live electrics.

• Don't keep pressing reset. Repeated resets can make a fault worse.

• Don't pour boiling water on pipes or use a naked flame to thaw them.

• Don't use a gas cooker or oven to heat the room, as it can build up carbon monoxide.

• Don't let anyone work on your boiler who isn't on the Gas Safe Register, the official list of engineers allowed to work on gas appliances. Our post on choosing a Gas Safe engineer explains how to check.

Keeping warm while you wait

A plug-in electric heater will keep one room comfortable. Keep it clear of curtains and don't leave it on overnight. If you have a hot water cylinder with an immersion heater, you can switch that on for hot water. Close curtains and internal doors to hold in the heat, and check on older relatives or neighbours if they're without heating too.

What to tell the engineer when you book

Having this ready helps the right part arrive on the first visit:

• the boiler's make and model, and any fault code

• what happened before it stopped, such as noises, leaks or the pressure dropping

• the pressure gauge reading

• whether you still have hot water

• the checks you've already made

What happens on a repair visit with us

Every boiler repair we carry out is done by a Gas Safe registered engineer. We confirm the make and model, run fault checks and explain what's wrong before we start. We carry common spares, and when a part has to be ordered we source it as quickly as we can. One customer, left with no heating or hot water in minus seven degrees, wrote that we "had to order parts and came back the same day to finish the job." As Baxi approved installers we can get genuine parts for Baxi boilers. Before we leave, the boiler is tested and you get a written report of what we found and fixed.

Many winter breakdowns start as small faults that an annual boiler service would pick up, so autumn is a good time to book one.

If your boiler has stopped and these checks haven't brought it back, Welm Facilities Maintenance Ltd can find the fault and get your heating running again. Book a visit through our boiler repair service and we'll tell you when we can be with you.