10 common boiler problems - what you can do about them

Your boiler is the heart of your home, so keeping it running efficiently is important. But things don’t always go to plan - and that’s where we're here to help.

Whether you’re worried about your boiler pressure being too high or too low, unusual noises, or even water leaks, don’t panic. We’ll do our best to help you find the problem and get your central heating system back up and running quickly.

Below, we've listed some of the most common boiler issues and outline their potential causes and their possible fixes:

• The pilot light keeps going out
• The boiler is making kettling noises (gurgling, whistling or banging)
• No heating or hot water
• Boiler is leaking
• Low boiler pressure
• Boiler not heating radiators
• Boiler smells
• The boiler is not responding to the thermostat
• Frozen condensate pipe
• The boiler keeps turning off

If you want peace of mind, check out our boiler cover plans. We've teamed up with Domestic & General to offer you a range of products for your boiler and home to suit your needs and budget.

View our BoilerCare plans

Quick summary

1. Pilot light keeps going out

The pilot light is a continuously lit, small flame on your boiler. It's fuelled by gas and is used to ignite the main burner when heat is needed for your hot water or central heating. The pilot light going out is a really common problem.

Potential causes 

This issue could be caused by something as simple as a draught blowing the flame out or a build-up on the gas nozzle. Alternatively, a broken thermocouple could be stopping the gas supply. The thermocouple is a safety device in the boiler that detects any temperature change in your pilot light, so it knows if the pilot light goes out.

What to try

Check that your other gas appliances are working. If they're not, contact your gas supplier. If your gas supply is okay, try reigniting the pilot light by following your boiler manufacturer's instruction manual. If you've lost the instructions, you can usually find them on the boiler manufacturer's website. This fault is more common with older boilers, as modern systems are not built with pilot lights and ignite electronically. 

When to call a boiler engineer

If the issue with your pilot light persists, it may be worth calling a boiler engineer to get a new boiler installed.

2. Boiler is making noises 

Strange noises coming from your boiler can be alarming, but don't worry - it's not normally a dangerous issue. It's best to resolve them as soon as possible, though, to avoid further damage to your heating system.

Kettling (banging/whistling sounds)

Potential causes

The top causes of boiler kettling are leaks in the boiler system, limescale build-up, and overheating or a faulty thermostat.

What to try

Check your system for any leaks, starting with the area around your boiler and the pipework beneath it. If that all seems okay, inspect all the radiators in the house, paying attention to the joints between pipes. 

Can't find any leaks? Check whether your area has hard or soft water. If you're in a hard water area, your pipework may be more susceptible to limescale build-up, which can restrict water flow and cause the kettling sounds. If it doesn't seem to be either of these, overheating might be the cause. Try adjusting or resetting your thermostat and you may be able to silence the boiler noise yourself.

When to call a boiler engineer

If you did find a leak, you'll need to arrange a boiler repair. A simple, external leak can be repaired quite easily; however, if it's an internal leak, you may need a new boiler - but our Gas Safe engineers will help diagnose the problem and get you back up and running. If you think limescale build-up is the issue, call an engineer to perform a chemical clean or power-flush to clear out the deposits. 

Gurgling

Potential causes

Gurgling sounds are usually a sign that there's some trapped air in your heating system.

What to try

Feel your radiators for any cooler patches on their surfaces. If you find some, it's likely that there is a pocket of trapped air there, stopping the water flow from heating it up. Turn your heating off and bleed your radiators to resolve the issue. 

When to call a boiler engineer

If the gurgling sounds persist after you've bled all your radiators, it's best to get a professional in to identify the cause of the sound.

3. No heating or hot water

Your boiler is a key part of your home, and you should be able to rely on it to help provide your home with heating and hot water.

Potential causes 

There are likely to be several causes for this fault – many of which we discuss in this blog, like a faulty pilot light, a leak or low pressure. In some cases, you'll require a replacement part to fix the problem.

What to try

There's not usually one single issue that can lead to your boiler failing to provide heat or hot water. However, you should start by checking that there are no issues with your boiler's pressure or thermostat. 

When to call a boiler engineer

If you can't find any issues with the pressure or thermostat that you can resolve yourself, you'll need to call an engineer to diagnose the issue. Give us a call on 0800 497 0705⁽¹⁾ for an emergency repair.

4. Boiler leaking

Water leaks in your boiler aren't usually immediately dangerous, but it's best to get them fixed urgently so they don't start causing bigger problems.

Potential causes 

Causes can vary, depending on where the leak or drip is coming from. A leaking system can result from a broken component, such as a seal or valve. It could also be the result of corrosion. 

What to try

Turn off the boiler's electricity supply as soon as you discover a leak to reduce the chances of any damage to live wires. It's also wise to check the boiler pressure gauge - if the arrow is in the red zone, water could be escaping from the pressure relief valve. Check that the filling loop, key or lever isn't stuck open, then wait for the system to cool before bleeding your radiators to release any pressure.

When to call a boiler engineer

If bleeding your radiators doesn't resolve the leak, call an engineer to repair your boiler. Never try to fix a faulty boiler yourself.

5. Low boiler pressure

If your boiler's pressure gauge shows a reading lower than one, you may have a problem.

Potential causes

Boiler pressure can drop due to leaks in the system, faulty pressure valves, or air escaping from radiators.

What to try

Inspect for leaks in the system. If you find a leak, check above for what the next best steps are. If there are no leaks, you can try re-pressurising the system. Check out our boiler pressure guide for detailed steps on how to do this.

When to call a boiler engineer

If there is still no improvement, you should call an engineer, as there's likely a failed component in the system.

6. Boiler not heating radiators

When your boiler is running, but the radiators aren’t warming up properly, it can be frustrating and leave your home feeling cold. This issue is fairly common in central heating systems, and fixing it can be straightforward.

Potential causes

If your radiators are only partially warm, or only some of them are working, the most likely reason for this is trapped air in the central heating system.

What to try

Turn your heating off and allow the system to cool down before bleeding your radiators to allow the trapped air to be released.

When to call a boiler engineer

If there's no improvement after bleeding them, the system might need flushing – this needs to be carried out by a professional central heating engineer.

7. Boiler smells 

A boiler should normally be odourless, and any unusual smell coming from it is a sign of a problem.

Possible causes

A rotten egg smell usually means a gas leak, which can be extremely dangerous as it could lead to fires, carbon monoxide poisoning or even an explosion. If you think you have a gas leak, it's an emergency, and you need to act fast.

What to do

Turn off your gas supply at the meter straight away - find the emergency control valve, it's normally a red or yellow lever in a meter box outside with the gas meter. If it's not there, it could be under your stairs, kitchen sink or in the garage. Don't switch anything electrical on or off, and open all doors and windows to get some fresh air into your home. Make sure you get out of the house, and don't light any naked flames, as even a small spark could cause an explosion.

When to call an engineer

You should call the National Gas Emergency line immediately on 0800 111 999. This number is free to call.

8. Boiler not responding to thermostat 

A faulty thermostat can sometimes cause problems in an otherwise healthy system.

Possible causes

If you have a wired thermostat, there might be issues with the wiring like a damaged component. For wireless thermostats, the batteries might be running low. 

What to try

Reset your thermostat. Sometimes, an accidental knock can switch off or change the thermostat's settings. If it's battery-operated, try replacing the batteries.

When to call a boiler engineer

If your thermostat settings seem okay, but the temperature is not, call an engineer, as it could be time to replace your thermostat.

9. Frozen condensate pipe

If you have a condensing boiler, it has a pipe that carries condensate (acidic water) to an external drain. It's usually white or grey plastic and is connected to the bottom of your boiler, running through the wall, outside your property.

Possible causes

Sometimes, in cold weather, a condensate pipe can freeze, causing noise in the pipes and no heating or hot water in your home. Your boiler should have a fault code notifying you when its condensate pipe is frozen.

What to try

First, check that the pipe is actually frozen by looking for fault codes (refer to your boiler manual for the relevant code) on the boiler's display screen. Locate the blockage - it'll usually be on the most exposed point, typically at the end of the pipe, just below the drain, or around any bends. You can check for frost to confirm it's frozen. To defrost it, you can pour warm water along the blocked area, or place a hot water bottle against it. Don't use boiling water, though, as this could make the pipe burst!

There are tutorials online that show you how to thaw a condensate pipe safely, if you'd prefer to follow along visually.

When to call an engineer

If you're not fully confident in thawing the pipe yourself, you should call a registered engineer to do it for you.

10. Boiler keeps turning off

Possible causes

This can be caused by various issues, such as a thermostat problem, low water pressure, or a lack of flow.

What to try

Check the pressure and thermostat as suggested above in issues five and eight.

When to call an engineer

If adjusting the thermostat, bleeding the radiators and/or re-pressurising the system fails, call a registered boiler engineer to repair your boiler.

How to prevent boiler problems

We recommend checking for issues periodically - check the pilot light is lit, look for any signs of leakage, and make sure your radiators are warm from top to bottom. It's also good to switch the heating on and run a boiler check in the summer months to prevent the system from seizing up whilst you're not using it.

Keeping up with your boiler maintenance is key to preventing potential issues. Get it serviced annually to make sure it's running as efficiently as possible and keep your warranty valid. Servicing your boiler will help you pick up any problems before they develop into something bigger. Check out our boiler maintenance and support plans to give you peace of mind that your boiler is always looked after.

Are you having boiler problems?

The best way to deal with boiler problems is to be proactive. You can save money and avoid stress in the long run by protecting your heating system or boiler with our maintenance and service plan. These include a yearly service.  
Need a new boiler? That's why we have trusted partners to provide Gas Safe engineers across the UK to help with your new boiler.

Get a new boiler    Compare boiler cover plans

Looking for boiler alternatives?

Want to be rid of boiler problems for good? Consider installing an air source heat pump instead. They're highly efficient, low-carbon and could lower your electricity bills in the long run.

Get an air source heat pump