Boiler problems - when is it time to call the experts?

If your boiler's broken, you may need to call in a professional. But when's the right time to do so? Here's how to determine whether you can fix your boiler yourself, or whether it’s time to call in professional help.

Written by Ben Gallizzi, Senior Content Editor - Energy and Electric Vehicles

Updated on 29 September 2026

How to troubleshoot common boiler problems

Some problems are easier to tackle than others. Before calling an engineer, see whether your problem is covered below and whether you may be able to fix it yourself.

1. My boiler is leaking

This can be down to multiple causes. Common reasons include:

Broken valve or seal
Poorly installed pipework
Leaking boiler pump
Corrosion
High temperatures
High water pressure

The last two reasons can be traced to the boiler’s safety valves: the pressure relief valve, which reduces water pressure and the temperature relief valve, which combats high temperatures. Both are designed to pass water as a safety precaution.

How to fix: In all cases, you’ll need to call an engineer to diagnose and fix the problem.

The easiest way to cut your energy costs is through insulation and draught-proofing. Insulation starts with the boiler unit itself, as well as any pipes. A well-insulated boiler tank will retain heat, saving you a fortune on reheating costs, but you can also insulate your pipes to minimise any heat loss at the source. Check out our guides to insulating your home to minimise energy costs.

2. My hot water is working but no heating

If your boiler is working but there’s no heating, then check the following:

If you have a combi boiler, check it’s not set to hot water only. This setting is commonly used during the summer months.
Check your heating controls to see when your boiler is set to switch on – make sure the clock is correct, and that you’ve set the heating to come on at expected times.
Check to see if there’s hot water in the pipes leading to your radiators – if there is, and the radiator is warm at the bottom, but cold further up, it’s likely they need bleeding to remove any trapped air.

Conversely, if your heating works but your hot water doesn’t, this may indicate a faulty diverter valve. When working correctly, the valve closes to divert hot water to taps, showers and other outlets when required, then opens back up to resume heating your radiators.

How to fix: You can attempt to fix the first three possible causes yourself, but if you have a faulty diverter valve, you’ll need a Gas Safe-registered engineer to fix the problem.

3. I’m getting no hot water or heating

Check the following if your boiler is failing to come on or provide any kind of heating:

Pilot light may be out or faulty
Your condensate pipes may have frozen
There may be issues with your thermostat (see below)
A diverter valve may be faulty (see above)
Your boiler’s pressure is too low – try repressurising it (see ‘My boiler keeps switching off’ below) before calling out an engineer

4. My boiler makes a noise when it’s switched on or off

Don’t worry unnecessarily. It’s normal for your boiler to make certain noises when it comes on or off – for example, the sound of the pilot light igniting or the pump circulating water through the heat exchanger. However, do take notice if noises occur at other times. Pay particular attention to:

Whistling sounds and banging noises

This is due to boiler kettling, which occurs when the water flow slows. This causes it to heat to boiling point rather than the temperature set by your boiler, which in turn leads to steam entering the system. Causes include limescale build-up, a faulty thermostat on the boiler (more common in older boilers) or a damaged pump.

How to fix: In all cases, you’ll need to call out a Gas Safe accredited engineer to diagnose the exact cause and suggest a remedy.

Gurgling noises

This happens when air gets trapped in the system and mixes with the water.

How to fix: Check your radiators to see if they need bleeding. If they don’t, and it’s particularly cold outside, check that the condensate pipe hasn’t frozen.

Droning noises

Does your boiler sound like an aeroplane is taking off? This is usually caused by a faulty pump.

How to fix: Call out a qualified, Gas Safe-registered boiler engineer.

Humming noises

These can be traced to excessively high water mains pressure, a pump sending hot water through the system too fast, or even the bearings in the boiler fan.

How to fix: Another job that requires an engineer callout.

Whooshing noises

This is typically caused by one of two reasons: a blockage in the air intake pipe or a blocked air filter.

How to fix: Again, this will require an engineer callout.

5. My boiler doesn’t respond to the thermostat

How to fix: Start by verifying your thermostat isn’t set too low – nudge it up a couple of degrees above room temperature, which should kickstart it into action. If the thermostat is battery-powered, check the batteries don’t need replacing; if it’s mains-powered, verify the clock hasn’t been reset by a recent power outage, which would knock its timings off. Also, check the switches haven’t been accidentally knocked out of position, and see if there’s a reset button or instructions in the thermostat’s manual.

If, after all these checks, the thermostat still isn’t working, it may be faulty. This is best handled by a registered heating engineer.

6. My boiler keeps switching off

Three major reasons for this include:

A problem with the thermostat (see above)
Low water pressure
Lack of flow

How to fix: After checking your thermostat and whether the radiators need bleeding, check the pressure shown on your boiler. If it’s too low or too high, follow our guide to repressurising the boiler; if that doesn't work, you’ll need to call a Gas Safe registered engineer to fix the problem.

7. My boiler won’t turn on

If your boiler won’t switch on at all, and you’ve determined the trip switch or fuse isn’t to blame, the problem is likely the boiler’s PCB board. PCB board problems can also manifest themselves in other ways, such as the interface not lighting up, flashing or displaying a specific error code.

How to fix: While you may be able to fix some errors yourself – for example, memory faults require you to consult your boiler manual for instructions on how to synchronise the PCB with the boiler – others require you to call out an engineer with Gas Safe accreditation.

How do you diagnose a boiler problem?

Try following these steps:

Examine your boiler’s on-screen display. It may have thrown up an error code – if it has, check your boiler manual for what this code means and the steps required to fix it.
If your boiler has a timer, check it’s correct – it may have been reset after a power cut, meaning you may need to set it up again.
If there’s no power going to the boiler at all, check the fuses to see if your boiler fuse has tripped. If the issue persists after fixing it, you may need to call an electrician to investigate further.
If you’re on a Pay As You Go tariff, make sure your prepayment gas meter hasn’t run out of credit.
If there’s no gas supply, or you can smell gas, call the National Gas emergency number on 0800 111 999.
If your boiler is working, but exhibiting signs of pressure problems, check its pressure gauge. If it’s lower than one you may have a problem. Check for leaks in the system, then repressurise it as outlined in your boiler manual.

How to prevent issues before they happen

Prevention is always better than cure, particularly with your boiler, where a little ongoing maintenance can save you a lot in boiler repair bills down the road. What's more, maintaining a boiler is easy. If you sign up for a boiler cover plan that includes an annual service check, you can ensure a Gas Safe Registered engineer inspects your boiler at least once a year.

Here are some other preventative tips to help keep your boiler working:

Many boilers can freeze up during prolonged spells of cold weather. One way to resolve this is to leave your boiler on permanently when temperatures dip below zero.
You don’t need to have the heating on full blast, but instead of letting it come on and off as required, you can set your programme to reduce the temperature to a minimal level.
A good timer system will allow you to set up different programme configurations, so you can set this up in advance and only activate it when the mercury drops.
Alternatively, focus your attention on the pipes themselves. Any external pipes, including the condensate pipe on a condensing boiler, can freeze in cold weather.
A short-term fix is to pour hot (but not boiling) water onto the pipe to warm it up and melt any frozen liquid inside. You may have to repeat this several times.
A potentially better solution could be to insulate the pipes or, where possible, move more of the pipe indoors.

What to look for when it comes to heating cover

There are many different levels of boiler cover available, ranging from simple breakdown cover for your boiler to a plan that protects the whole central heating system. You should also check to see how much cover each plan offers, as boiler cover typically limits payouts to a maximum amount that usually range from £1,000 to £1,500.

You can only get boiler cover if you own the home so don't try and take it out if you're renting, although you could ask your landlord to take out cover if there are persistent problems.

You will also have limited options available if you try to get boiler cover on a boiler that's more than 15 years old as some insurers don't cover older models.

Find out how to choose the right boiler insurance here.

FAQs

Who should you call when you have boiler problems?

If your boiler is still under warranty, call the manufacturer who should send a service engineer to your home. If it’s out of guarantee, you’ll need to call a reputable engineer that’s Gas Safe accredited. You can find locally accredited engineers through the Gas Safe Register website.

What is the biggest cause of boiler breakdowns?

Old age and lack of maintenance. Over time, rust and corrosion build up in components, pipes and connections. You can extend the life of your boiler through regular servicing. You can pay for this separately or look for boiler cover plans that include an annual service in the price.

Can a faulty boiler cause high gas bills?

Yes, because it’s being forced to work harder making it less efficient. More importantly, however, it may lead to more serious problems, including potential carbon monoxide poisoning. Get it checked out by a Gas Safe-registered engineer as a matter of urgency.

How much does it cost to replace boiler parts?

Many parts, such as the diverter valve or PCB board, run into hundreds of pounds (not including labour). If the cost of repairs mount or your boiler is out of warranty, it might be more cost-effective to invest in a new boiler instead.