What to do if your boiler breaks down at Christmas

Boiler issues in the depths of winter are bad enough, but what should you do if they crop up over the Christmas period?

The best way to avoid a cold Christmas as a result of a boiler breakdown is to spot the warning signs when they first arise. If you're unsure what to look out for – or if you suspect your boiler is already on the blink – read on. 

We asked a number of popular boiler manufacturers what consumers could do if their boiler decided to play up at Christmas. Vaillant and Viessmann responded to our questions. 

Here's a round-up of what they recommend, plus our advice, on what to do if your boiler packs up on the big day. 

Need a new boiler entirely? Make sure that you pick from one of the best boiler brands, rated for customer satisfaction, engineer recommendation, reliability and more. 

Signs that your boiler is about to break down

Darren McMahon, marketing director at Viessmann, told us: 'It's often fairly obvious when your boiler has broken down because it either won’t be supplying heat to your radiators and taps or it won’t turn on at all. But sometimes, it’s not as easy to spot.' 

Other signs your boiler is faulty include:

• Funny noises, including banging, tapping, clicking or knocking.
• An unusually high gas bill.
• A yellow or orange pilot light.
• Pressure issues (either too high or too low).
• A leak in the pipes around the boiler.

If you notice any of these and your boiler is still working, it could be a sign that it’s about to break down. It's better to act on any concerns before they become an emergency.

Find out how Vaillant, Viessmann and other companies such as Baxi, Glow-worm and Worcester Bosch compare in our guide to the best boiler brands 

First, check the boiler fault code 

If your boiler is acting up and is displaying a fault code, that's a helpful start. Most manufacturers have guides on their website or user manual to help you understand what different fault codes mean. 

For example, the Viessmann fault code checker explains that an OC fault code on the Vitodens 100-W boiler means there's insufficient power being supplied. 

Even if there's no fault code, manufacturers’ websites usually have guides on simple adjustments that can you can make if you know what's gone wrong, so this should be your first port of call.

If that's no help, read on to find out about some common problems and their causes and fixes. 

Remember that you should never attempt to make repairs that require a registered gas engineer.

Worried about how to afford a new boiler? Find out if you could be eligible for a free boiler or boiler grant

Identifying what's wrong with your boiler

There are numerous reasons why boilers might break down, as they contain lots of parts. But these are the most common reasons, according to Viessmann: 

• no power supply
• no gas supply
• no water supply
• low or high pressure
• frozen condensate pipe
• faulty thermostat
• no pilot light
• faulty or broken controls (diverter valve).

Some of these issues you can fix yourself, whereas others require the assistance of a heating engineer. 

Given you may be hard pushed to find a boiler engineer to come out on Christmas Day, and you could well face a hefty out-of-hours call-out charge, your first step is to see if there's an easy fix. 

1. No power supply to your boiler

Electricity is essential for your boiler to work. Check if it has an electricity supply by looking at the digital or LCD display. 

Things that could cause a disruption to the power supply include a power cut, a tripped fuse in the main electrics box, a broken circuit board or even no credit in your account if you have a prepayment meter. Someone may have turned off the boiler’s electrical supply manually by accident, so check the wall socket where it's plugged in. 

Also check your fuse box and make sure that all fuses are active.

It could be that your boiler does currently have power, but something like a power cut has disrupted its programming.

You can press reset on the boiler and leave it off for 10 minutes. Switch it on again and make sure that the date and time are correct, as well as your preferred program – you may need to consult a user manual or manufacturer website to work through these steps. 

If you’ve done all of these things and the boiler still seems to be broken, you may need to contact a Gas Safe registered engineer to take a look. It could be that the issue is coming from a broken circuit board and this issue cannot be fixed by you.

5 signs that you need a new boiler: telltale signs that you shouldn't dismiss  

2. Boiler leaks

Vaillant says that this is one of the most common boiler issues to occur. 

Water leaking from your boiler can cause water damage to your home and ruin the electrical components in and around the boiler, causing it to malfunction. 

You should always treat a boiler leak seriously. You shouldn't remove the boiler casing yourself. 

If you find a leak, you should call a qualified heating engineer as soon as possible to investigate. 

Some boiler companies will have recommended engineers listed on their websites, or you can head to Which? Trusted Traders to find a vetted trader.

3. Low boiler pressure

Low boiler pressure can lead to cold radiators and a lack of hot water. Your boiler's display panel will show its pressure, either as part of a digital display or a physical dial showing the level of pressure in the system. 

Usually, the pressure of a boiler should be around 1.5 bars, with slight variance depending on the boiler manufacturer and model.

Often the pressure can be readjusted by opening the boiler filling loops underneath the appliance. It's quick and easy to do yourself, but always refer to your instruction manual first.

4. Frozen condensate pipes

Condensate pipes are used to transport waste water out of your boiler system during the condensing process. If the pipe is external, this water can freeze when temperatures drop. 

This can often force the boiler to shut down automatically as a precautionary measure.

The safest way to unfreeze the pipe is to pour warm (not hot) water over it and wrap it in a towel or blanket. 

Head to our guidance on how to thaw a frozen condensate pipe to find out more.

What to do if you're not sure why your boiler isn't working

We have more information in our guide to common boiler problems and repair costs.

If you're still unsure, contact a heating engineer. Try the company that installed it or a Which?-vetted Trusted Trader. Call-out charges are likely to be a lot higher on Christmas Day, and you may need to phone around. 

If you can't get hold of a Trusted Trader or an engineer from your boiler company, make sure you don't get stung by a rogue trader profiting from your desperation to get the problem fixed. 

Search the company's name to check reviews online (not just the ones listed on the company's own website) and, as a bare minimum, make sure they are Gas Safe registered. 

The Gas Safe Register has a tool for finding engineers who are legally allowed to carry out gas works. 

A reputable engineer should also be able to confirm their call-out charge (not including any remedial works) before arriving. 

What to do if you smell gas

If you smell gas, it could be a more serious problem than you think. 

If you ever smell gas, regardless of whether you know it's coming from your boiler or not, you should call the National Grid gas emergency line immediately on 0800 111 999. 

If you're a British sign language (BSL) user, you can use SignLive to contact the National Gas Emergency Service free of charge. 

How to avoid a future boiler breakdown

Keeping up with routine boiler servicing is the best way to identify problems early and avoid any emergencies. If you haven't had one in the past 12 months, book one in with a heating engineer. 

Find out more about getting a boiler service and the key questions to ask your engineer to make the most of their time.

Many new boilers come with apps with preventative maintenance features, helping to avoid breakdowns in the first place. Such apps mean the installer gets an alert if the boiler is not running optimally or needs a new part. They can then get in touch with the homeowner to suggest a repair is due, before being caught out.