Boiler Not Working: Causes & Solutions

The most common reasons your boiler is not working include low boiler pressure, a frozen condensate pipe, thermostat issues, ignition failure, a faulty diverter valve, or an airlock in the system. 

The good news is that many of these problems have straightforward fixes, and knowing what to look for can save you both time and money.

What Causes a Boiler to Not Work?

There are several reasons why a boiler stops working, ranging from simple fixes you can handle yourself to more serious faults that require a Gas Safe registered engineer. Understanding the root cause is the first step to getting your heating and hot water back up and running.

Low Boiler Pressure

Low boiler pressure is one of the most frequent reasons a boiler stops working. Most modern combi boilers need a pressure reading of between 1 and 1.5 bar to function correctly. If the pressure drops below this, your boiler may shut itself down as a safety measure. 

You can check the pressure gauge on the front of your boiler, and if the needle is sitting below 1, low pressure is likely the culprit.

Low pressure is often caused by a small water leak somewhere in the system, a recently bled radiator, or a pressure relief valve that has discharged.

How to Fix Low Boiler Pressure

1. Locate the filling loop on your boiler, which is usually a silver or grey flexible hose beneath the unit.
2. Make sure both ends of the filling loop are securely attached.
3. Slowly open both valves on the filling loop, allowing cold mains water into the system.
4. Watch the pressure gauge rise and close both valves once the needle reaches 1.5 bar.
5. Switch your boiler back on and monitor it over the next few hours.
6. If the pressure keeps dropping, contact a Gas Safe engineer as there may be a leak in the system.

A Frozen Condensate Pipe

A frozen condensate pipe is an extremely common cause of boiler failure during winter. Condensing boilers produce acidic condensate water as a by-product, which drains away through a plastic pipe that often runs outside. 

When temperatures drop below freezing, this pipe can freeze solid, causing the boiler to shut down and display a fault code.

How to Fix a Frozen Condensate Pipe

1. Locate the condensate pipe, which is usually a white or grey plastic pipe running from your boiler to an outside drain or wall.
2. Pour warm (not boiling) water over the frozen section of the pipe to thaw it gently.
3. You can also use a hot water bottle wrapped around the pipe to melt the blockage.
4. Once thawed, reset your boiler by pressing the reset button and holding it for a few seconds.
5. If your boiler fires back up, monitor it closely over the next day.
6. To prevent it from happening again, consider insulating the pipe with foam lagging, which is inexpensive and available at most DIY stores.

Thermostat Problems

Thermostat problems are a surprisingly common reason for a boiler not working as expected. If your thermostat is faulty, has dead batteries, or is incorrectly programmed, it may not be sending the right signal to your boiler to fire up. 

This can make it seem as though your boiler has broken down, when in reality the issue is with the controls rather than the boiler itself.

How to Fix Thermostat Problems

1. Check that your thermostat is switched on and set to a temperature above the current room temperature.
2. Replace the batteries if your thermostat is wireless or battery-operated.
3. Check the programmer or timer settings to ensure your heating schedule is correct.
4. If you have a smart thermostat, check the app to ensure it is connected to your Wi-Fi and functioning properly.
5. Move your thermostat away from heat sources like radiators or direct sunlight, as this can cause false readings.
6. If the thermostat appears to be working but your boiler still does not respond, call a heating engineer to test the unit.

Ignition Failure

Ignition failure means your boiler is attempting to fire up but cannot establish a flame. This is a fairly common boiler fault and can be caused by a faulty ignition lead, a dirty or damaged burner, or issues with the gas supply itself. Most boilers will display a fault code or lockout light when ignition fails.

How to Fix Ignition Failure

1. First, check that your gas supply has not been interrupted. Check other gas appliances in your home, such as your hob, to see if they are working.
2. If the gas supply is fine, try pressing the reset button on your boiler and see if it fires up.
3. Do not attempt to reset the boiler more than two or three times in quick succession, as this can cause damage.
4. If the boiler continues to fail to ignite, do not attempt to investigate the gas components yourself. Always contact a Gas Safe registered engineer.
5. A qualified engineer will inspect the ignition leads, electrode, and burner assembly for wear or damage.

A Faulty Diverter Valve

A faulty diverter valve is a common issue in combi boilers and can result in either no hot water, no central heating, or sometimes both. The diverter valve controls the flow of hot water between your taps and your radiators. When it gets stuck or wears out, it cannot direct water to the right place, leaving you without heating or hot water.

A classic sign of a faulty diverter valve is when you have hot water from your taps but no heating, or vice versa.

How to Fix a Faulty Diverter Valve

1. Check whether you have hot water but no heating, or heating but no hot water, as this helps narrow down the issue.
2. Try resetting your boiler to see if this temporarily frees a stuck valve.
3. Do not attempt to replace a diverter valve yourself, as this is an internal boiler component.
4. Contact a Gas Safe registered engineer who can test and replace the valve if necessary.
5. Depending on the age of your boiler, your engineer may advise whether it is more cost-effective to repair or replace the unit.

Kettling Noises and Limescale Buildup

Kettling is when your boiler makes a rumbling, banging, or whistling noise, much like a kettle boiling. This is typically caused by limescale or sludge building up on the heat exchanger, which restricts water flow and causes overheating.  common boiler noise issues explained can help homeowners identify and address these troubling sounds. Understanding the causes behind these noises can lead to more effective preventative measures, ultimately prolonging the life of the boiler. Additionally, recognizing when professional maintenance is necessary can save time and reduce costly repairs in the long run.

Kettling is particularly common in hard water areas of the UK, such as London, the South East, and the Midlands.

How to Fix Kettling and Limescale Buildup

1. Contact a heating engineer to carry out a powerflush, which involves pumping a cleaning solution through your central heating system to remove sludge and debris.
2. Ask your engineer to add a central heating inhibitor to the system after the flush, which helps prevent future sludge buildup.
3. Consider fitting a magnetic filter to your boiler, which catches iron oxide particles before they can accumulate.
4. In hard water areas, a scale reducer or water softener can help prevent limescale forming on the heat exchanger.
5. Have your boiler serviced annually to catch early signs of limescale buildup before they become a bigger problem.

No Hot Water but Heating Works

If your heating is working fine but you have no hot water, this is a specific fault pattern that points to a handful of likely causes, including a faulty diverter valve (covered above), a broken motorised valve, or an issue with the hot water cylinder if you have a traditional system boiler setup.

How to Fix No Hot Water 

1. Check your boiler’s programmer and thermostat settings to ensure hot water is scheduled to come on.
2. If you have a cylinder, check the cylinder thermostat is set to around 60 degrees Celsius.
3. Try resetting your boiler to clear any minor faults.
4. If the problem persists, call a Gas Safe engineer to inspect the diverter valve or motorised valve.

Boiler Keeps Switching Off

A boiler that keeps switching itself off is a clear sign that something is not right. This is often referred to as “short cycling” and can be caused by low water pressure, a faulty pump, a blocked heat exchanger, or an issue with the thermostat. 

While it might seem like a minor inconvenience, a boiler that keeps cutting out will leave your home cold and can cause further wear on components over time.

How to Fix a Boiler That Keeps Switching Off

1. Check the pressure gauge and repressurise the system if the reading is below 1 bar (follow the steps in the low pressure section above).
2. Check that the thermostat is not set too high, as this can cause the boiler to overheat and cut out.
3. Ensure radiators are bled and there are no airlocks in the system that could be restricting flow.
4. If the problem continues, a Gas Safe engineer will need to check the pump, heat exchanger, and any relevant fault codes.

How Can You Prevent Boiler Issues?

Preventing boiler problems is far easier and cheaper than dealing with an unexpected breakdown. A few simple habits can keep your boiler running reliably throughout the year.

1. Book an annual boiler service with a Gas Safe registered engineer to catch small issues before they turn into expensive repairs.
2. Check your boiler pressure regularly and repressurise it when it drops below 1 bar.
3. Bleed your radiators once a year, ideally at the start of the heating season, to remove trapped air from the system.
4. Insulate your condensate pipe before winter arrives to reduce the risk of freezing.
5. Add a central heating inhibitor to your system to prevent sludge and corrosion building up inside the pipework and boiler.
6. Leave your heating on a low setting during very cold spells rather than switching it off completely, to keep pipes from freezing.
7. Invest in a boiler cover plan so that when a fault does occur, you are not left facing a large, unexpected repair bill. PlusHeat’s boiler cover plans are designed to give homeowners and landlords peace of mind all year round, with fast access to qualified engineers whenever you need them. 

Get Year-Round Peace of Mind With PlusHeat Boiler Cover

No matter how well you maintain your boiler, faults can and do happen at the worst possible times. Whether it is a cold snap in January or a pipe issue in the middle of the night, having the right cover in place means you never have to worry about the cost of calling out an engineer or sourcing replacement parts.

PlusHeat offers comprehensive boiler cover plans designed specifically for UK homeowners and landlords. Their plans include access to Gas Safe registered engineers, fast response times, and cover for parts and labour so that an unexpected breakdown does not turn into an unexpected expense.

Take a look at our boiler cover plans today and make sure you are covered before the cold weather hits.

Frequently Asked Questions

Can I use my boiler if it is showing a fault code?

It depends on the fault code. Some codes indicate a minor issue where a simple reset will resolve the problem. Others, particularly those related to gas pressure or ignition faults, mean the boiler is not heating water and has locked out for safety reasons and should not be used until a Gas Safe engineer has inspected it. 

Always refer to your boiler’s manual to understand what a specific code means.

How long does a boiler repair usually take?

Most standard boiler repairs can be completed within a few hours by a qualified engineer, particularly if the fault is straightforward and the parts are readily available. More complex repairs, such as replacing a heat exchanger, may take longer or require a return visit if parts need to be ordered. 

Having a boiler cover plan in place can speed up the process, as the engineer comes prepared with common parts.

Is my boiler more likely to break down in winter?

Yes, boilers tend to work much harder during colder months, which does increase the likelihood of a fault occurring. Frozen condensate pipes, pressure fluctuations, and the increased demand on the heating system all contribute to a higher rate of breakdowns between November and February. 

This is why it is worth getting your boiler serviced in the early autumn, before the heating season begins.

How do I know if my boiler needs replacing rather than repairing?

A good rule of thumb is to consider the age of your boiler alongside the cost of the repair. If your boiler is over 10 to 15 years old and the repair cost is more than half the price of a new unit, replacement is often the more sensible long-term investment. Newer boilers are also significantly more energy efficient, which can lower your gas bills considerably. 

A Gas Safe engineer can advise you honestly on whether repair or replacement is the better option.

What should I do if I smell gas near my boiler?

If you smell gas, do not attempt to turn the boiler on or off, use any electrical switches, or try to identify the source of the leak yourself. Leave your home immediately, leave the front door open, and call the National Gas Emergency Service on 0800 111 999 from outside or from a neighbour’s property. 

Do not re-enter your home until the gas has been declared safe by an engineer.