Boiler Not Working: A Homeowner’s Guide to Causes and Fixes of Boiler Breakdowns

A boiler not working is a serious equipment failure that often constitutes an emergency for a homeowner. A boiler not working on cold winter days means a lack of central heat and hot water, whilst a boiler that’s leaking natural gas or carbon monoxide represents a fatal risk for the home’s dwellers.

The types of breakdowns that result in a boiler not working are classified into the following three, broad scenarios.

• You have hot water but no heating: Getting hot water whilst the central heating doesn’t work may stem from three underlying issues. First, your pipes could be blocked by debris, a fault you can fix with a system flush. Second, the central heating system might have air locks, which are fixed by bleeding radiators. Third, you could have low system pressure, which you’re able to top up using the filling valve. Fourth, your boiler may be suffering from a pump failure, in which case you’ll need to call a professional.
• You have heating, but no hot water: Having a functional central heating system but no hot water is likely the result of a faulty diverter valve. You need a qualified engineer to repair a broken diverter valve.
• You have no hot water and no heating: A faulty gas valve, blocked burner, low gas pressure, broken fan, and an extinguished pilot light are all possible causes of a boiler that’s not working at all. All of the issues listed above require professional diagnostics and repairs from a qualified Gas Safe engineer.

Resetting your boiler is often necessary to get it working again after you’ve fixed the underlying cause of the breakdown. The restart procedure is similar for all boilers, but some nuances (such as where to find the reset button) vary between boiler models.

Boiler breakdowns are often pricey to fix. A boiler replacement is the more economical option in the long term when the boiler is old, out of warranty, and the repairs cost more than half the price of a boiler replacement. However, repairing the component is the more cost-efficient option if the boiler is new, under warranty, and the scope of repairs is not significant.

Why is my boiler not working?

The reason your boiler is not working differs depending on the type of service failure you’re experiencing. The most common boiler failures are grouped into the following three core categories.

• Boiler not heating water but radiators are working: When you have no hot tap water while the radiators remain hot, your boiler likely suffers from a faulty diverter valve or low system pressure. Low system pressure, in turn, is the likely result of a boiler leak. It’s often possible to repair a broken diverter valve, although sometimes a full replacement is needed. Low system pressure is easy to top up without calling a heating engineer. However, you should find and repair any leaks in the system first.

• Boiler provides hot water at the taps, but the radiators are cold: A scenario where you have hot water but the radiators are cold most likely stems from low system pressure or air locks in the radiators. Simple DIY fixes may be able to solve the problem as long as you don’t have a leak in the system.

• Boiler not turning on, resulting in no heating and no hot water: A boiler that’s producing neither heat nor hot water is a more serious situation. A boiler that’s not working at all likely suffers from a failed internal component, and the failure should be diagnosed and rectified by a Gas Safe heating engineer.

We explain all three scenarios of a boiler not working below in greater detail.

Heating works, but no hot water

Getting no hot water at the taps while the radiators remain hot typically means that a combi boiler is unable to change from the central heating to the hot water function. Combis rely on a diverter valve to switch between heating radiators and supplying domestic hot water for the taps (regular and system boilers do not have diverter valves).

Faulty diverter valve

A faulty diverter valve is the most likely cause if your heating works but you’re getting no hot water from a combi boiler. A diverter valve controls whether the boiler is heating water for radiators or taps at any given moment. Having no hot water at the taps likely stems from a faulty diverter valve that’s causing your boiler to function incorrectly.

It’s possible to determine whether the diverter valve is at fault by seeing whether the valve is in the cold water position. If it is, turn on the hot water and see if the valve moves to the hot water position. The diverter valve is likely the culprit if it remains in the cold water position even after you’ve called for hot water by turning on a tap.

However, diagnosing a broken diverter valve requires specialised knowledge and experience, so it’s best to leave the task to a Gas Safe heating engineer. The engineer may be able to repair the diverter valve if it’s simply seized in the wrong position. However, they would have to replace the valve altogether if it deteriorated due to wear-and-tear. The cost of replacing a diverter valve may or may not be covered by your warranty or boiler cover policy.

There’s hot water but heating is off

A seemingly faulty boiler that’s giving you hot tap water but not heating the radiators likely suffers from one of the four possible issues. Two of these problems that cause the radiators to stay cold relate to the central heating system rather than the boiler itself. Below are the four issues that may result in cold radiators even when the boiler is supplying hot water to the taps.

• Air locks: Air locks are pockets of air in the central heating system. These air pockets block hot water flow and prevent radiators from warming up. Air locks are a problem with the central heating system rather than the boiler.
• Low pressure: Low pressure in the heating system may cause inadequate hot water flow through the radiators, thus affecting their heat output levels.
• Boiler pump failure: A boiler pump that’s not working properly fails to circulate the hot water through the central heating system, thus causing your radiators to stay cold.
• Blocked pipes: Central heating pipes that are blocked with sludge or limescale prevent hot water from circulating and heating the radiators effectively. Blocked pipes are a central heating pipework issue, not a boiler problem.

Below we take a deeper look at the four issues behind a boiler that’s not heating radiators while hot tap water is present.

Air locks

Central heating air locks prevent hot water from flowing into the radiators. Air locks are pockets of air that are trapped in the central heating pipework and radiators. You have to bleed your radiators to rid the central system of the air locks and enable the radiators to heat properly. You’re typically able to bleed radiators yourself without needing expert assistance. Your radiators should be getting hot as required once you’ve released the air locks by bleeding the radiators and topped up the system pressure (if necessary).

Low pressure

Low pressure may prevent hot water from reaching all of your radiators, thus causing them to emanate less heat than required. Check the pressure gauge on your boiler and make sure the reading is between 1 and 1.5 bar. A boiler pressure reading below 1 bar while the boiler is in operation likely points to a leak in the boiler or the central heating system. You have to get a Gas Safe heating engineer to troubleshoot a leak that’s coming from the boiler. However, a plumber is able to fix the leak if it’s coming from the central heating pipework instead of the boiler. Your boiler pressure (and radiator heat) should return to normal levels once the technician repairs the leak and tops up the boiler.

Boiler pump failure

A failed boiler pump is unable to circulate hot water properly to your home’s radiators. A clear sign of a failed boiler pump is if your radiators are cold while the pump is making vibrating or unusual noises.

You should contact a Gas Safe boiler engineer as soon as possible if you’ve observed signs of a boiler pump that’s not functioning properly. The engineer may be able to repair the pump, but a full replacement is needed if the pump has undergone significant damage due to age, wear-and-tear, and debris accumulation.

Blocked pipes

The pipes that carry hot water to the radiators may be blocked, preventing the flow of hot water. These blockages are usually caused by limescale or sludge buildup. Sludge and limescale blockage affects all parts of the heating system and boiler. Such buildup causes more than just reduced hot water flow – it also damages the boiler’s internal components over time.

Removing debris from the central heating system requires a procedure known as a “flush”. There are several types of flushes available, and a qualified boiler engineer is able to determine which of these procedures is most appropriate in your situation. The radiators should be able to heat up sufficiently once there are no more blockages in the central heating system to disrupt the flow of hot water.

Boiler is not firing up

A boiler that won’t turn on at all likely suffers from one or more of the five problems listed below.

• Faulty gas valve: A faulty gas valve may be disrupting gas flow to the boiler, thus starving it of the fuel needed to fire up and operate.

• Blocked burner: A blocked burner might prevent the boiler from producing and maintaining a flame, thus causing the boiler to not work.

• Low gas pressure: Low gas pressure is a common cause behind boilers failing to fire up, as there’s not enough fuel for ignition to take place.

• Fan failure: A boiler automatically locks out if the fan fails to start. Fans are meant to expel toxic exhaust gases from the boiler, so their failure is a critical fault during which boilers are designed not to start up at all.

• Pilot light out: Older boiler models have pilot lights that ignite the main burner. A boiler locks out if the pilot light is damaged and unable to light the gas at the burner.

Faulty gas valve

A faulty gas valve may prevent the proper flow of gas to the burner, causing the boiler not to ignite. Gas valves regulate the flow of gas to the burner, so trying to repair or inspect a gas valve on your own is dangerous (and illegal). Always request the service of a Gas Safe heating engineer if you suspect that a faulty gas valve is causing your boiler not to work.

Blocked burner

A blocked burner is another possible cause of a boiler not working. A boiler’s burner could be blocked due to a build-up of debris or other obstructions that prevent the gas from flowing smoothly through the component. Find a Gas Safe heating engineer to inspect your boiler’s burner and recommend a course of action if you suspect that the burner blockage is causing the service disruption. The engineer may be able to disassemble and clean the burner, but you may need to get a replacement if the blockage is too severe and the burner is frail due to age.

Low gas pressure

Low gas pressure or a lack of gas could be the cause of a boiler not starting up as low pressure may not give the boiler enough fuel to start. You’re able to resolve the low gas pressure issue in two ways, depending on whether your boiler runs on natural gas or LPG.

• For natural gas boilers: Contact your gas supplier and ask if there are any known disruptions to gas service in your area.
• For LPG boilers: The most likely reason your LPG boiler gas pressure is low is that you’re running out of fuel. Check to see how much fuel is left and fill up the tank if needed.

Fan failure

Fan failures typically cause boilers to lock out. The fan is a critical safety feature that directs dangerous exhaust gases towards the flue, and internal failsafes shut down the entire system if no fan movement is detected. You’ll see a “fan fault” code on the display screen if the boiler’s fan stops working and causes a lockout. In this case, call a heating engineer to come and fix (or replace) the fan.

Pilot light out

A pilot light that’s out could cause a boiler not to turn on, as the pilot light is used to ignite the main burner in older boilers. Sensors detect if the pilot light goes out and shut down the system to prevent dangerous gas leaks. A Gas Safe engineer is able to repair or replace your pilot light and thus get the boiler to turn on.

How to restart a boiler?

The procedure needed to restart a boiler varies depending on the specific make and model. However, the vast majority of boilers share a similar restart protocol involving the 4 steps below.

• Locate your boiler’s reset switch or button. The reset button is usually found on the display panel of your boiler, and typically shows an icon of a crossed out flame.

• Press and hold the button. The usual minimum time for holding the reset button is around 10 seconds.

• Look to see if you have a flame. It typically takes about 2 to 3 minutes for a boiler to reset, so allow at least this amount of time before trying a second time. If you still have no flame, contact a professional.

• See if the boiler works. If the reset procedure results in a flame, check to see that the boiler is working properly. You’re able to check if the boiler is working by turning up the thermostat temperature and checking the temperature of the hot water at the furthest tap from the boiler.

Should I repair or replace a broken boiler?

Whether you should repair or replace a broken boiler depends on the 4 considerations below.

• Age of the boiler: It’s usually more cost-effective to replace your boiler with a new, more energy-efficient model if the existing boiler is more than 15 years old.
• Extent of the damage: Extensive damage, such as a cracked heat exchanger, generally costs a lot to repair. It may be more cost-effective to replace the boiler rather than repair it if it’s suffered massive damage to its internal components.
• Cost of repairs: Compare the cost of repairs to the cost of a new boiler. It may be more cost-effective to replace a broken boiler if the cost of repairs is more than half the cost of a new boiler.
• Energy efficiency: If your current boiler is not energy efficient and you’re paying high energy bills, it may be more cost-effective to replace it with a new, more energy-efficient model.

It’s best to consult with the engineer who has inspected your broken boiler and ask for their advice. However, you can get new boiler quotes on your screen now using Heatable – these quotes will give you an idea of what your preferred replacement boiler costs to fit.

How much does it cost to repair a broken boiler?

It costs between £50 and £1,500 to repair a broken boiler. The exact cost depends on the type of boiler, the extent of the problem, and the location of the repair. The following are 5 factors that affect the cost of boiler repairs.

• Type of boiler: The cost of repairs for a gas boiler is different from the cost of repairs for an oil or electric boiler.
• Extent of the damage: Minor repairs, such as replacing a faulty thermocouple, typically cost around £50 to £200. More extensive repairs, such as replacing a heat exchanger, cost £500 to £1000.
• Labour costs: The cost of labour varies widely depending on your location, the complexity of the repair, and the qualifications of the repair technician.
• Parts cost: The cost of the parts also varies depending on the type of boiler and the specific parts that need to be replaced.
• Inspection cost: Some companies may charge an inspection fee, even if you don’t proceed with the repair.

How much does it cost to replace a boiler that’s not working?

It costs anywhere between £2,000 and £5,000 to replace a boiler that isn’t working, including both the boiler and installation costs. The exact replacement costs of a boiler are influenced by the following five factors.

• Type of boiler: The cost of installing a combi boiler is different from the cost of a system boiler or a conventional boiler. Similarly, the prices for gas, LPG, electric, and oil fired boilers all differ, too.
• Size of your home: The cost depends on the size of your home, the number of radiators, and the type of heating system.
• Location of the installation: The cost of labour varies widely depending on your location, and the complexity of the installation.
• Brand and model of the boiler: the cost depends on the brand and model of the boiler, as some boiler models are more expensive than others.
• Warranty: The warranty offered by the manufacturer affects the total boiler replacement cost. Cheaper boilers may only come with a 2-year warranty, and high end models may have 12-15-year warranties.

Due to the potentially high costs of replacing a boiler, it’s a good idea to do as much research as possible about the fiscal implications of a new system. You can start researching your new boiler costs by getting a fixed-price online quote from Heatable.

Boiler not working FAQs

Below are answers to common questions about boilers not working.

What to do when your boiler is not working?

Below are the two things you should do when your boiler is not working.

• Attempt troubleshooting yourself: You may be able to troubleshoot several causes of your boiler not working without the aid of an engineer. Simple faults that have DIY fixes include gas or power supply issues and incorrect temperature settings.
• Call a qualified boiler engineer: Boiler faults that stem from the malfunction of an internal boiler component, or a leak in the system, need to be handled by a Gas Safe engineer.

What to check if my boiler isn’t working?

The following are five things to check if your boiler isn’t working.

• Fault code on the boiler screen: A fault code (also known as an “error code”) indicates which boiler part or function is not operating properly. You’re able to determine why your boiler is not working by looking up the error code. Then, you may decide to call a Gas Safe engineer (if the problem concerns an internal boiler part) or troubleshoot yourself (if the problem doesn’t stem from a broken component).
• Thermostat temperature setting: Your boiler may not fire up if the thermostat is set below 21°C. Try turning it above 21 degrees to see if the boiler starts.
• Boiler pressure: Most boilers lock out when the boiler pressure drops below 1 bar. A pressure reading of less than 1 bar generally means that there’s a leak in the system, so call an engineer to inspect the boiler before you top up the pressure. Topping up the boiler before you fix the leak does not resolve the core problem behind the pressure loss.
• Pilot light: Older boilers are fitted with a pilot light that ignites the gas flowing into the system. A malfunctioning pilot light is a possible cause of a boiler not working, and one that requires handling by a Gas Safe engineer.
• Fuse: Check to see whether the fuse has blown (or the circuit breaker has tripped), as a blown fuse would leave the boiler without power and unable to operate.

Can I fix my boiler myself?

No, you cannot fix your boiler yourself. You should not attempt fixing a broken boiler by yourself for three reasons. First, it is against the UK law for anyone who is not a Gas Safe registered engineer to work on gas appliances, including boilers. Gas Safe is the official gas registration body for the UK, and all engineers must be registered with them and carry a Gas Safe ID card. Second, improper DIY fixes jeopardise the safety of the boiler and put you and your family at risk. Third, fixing the boiler without a licensed, qualified technician typically voids the manufacturer’s warranty on the boiler.

However, you’re able to perform some basic troubleshooting if your boiler is not working. For example, you may check to see whether the temperature is set high enough, whether the pilot light works, and whether the boiler is getting its gas and power supply.

Should I switch my boiler off if it’s not working?

It’s a good idea to switch your boiler off if it’s not working. Turning a boiler that’s not working off ensures the safety of your family and your home and prevents further damage to the boiler’s components.

The following are two additional safety measures you should undertake once you’ve turned off a broken boiler.

• If you suspect a gas leak: Call the 24/7 National Gas Emergency Service on 0800 111 999 immediately if you suspect a gas leak. Do not attempt to fix the problem yourself and do not touch any electrical switches or use any naked flames.
• If you suspect a failed internal boiler component but no gas leak: Call a professional heating engineer who is Gas Safe registered to inspect and repair your boiler if you suspect that an internal component failure is causing your boiler to not work. Follow this step even if you have an electric or oil-fired boiler and you’re not sure what’s causing the problem.

Is a broken boiler an emergency?

It depends. A broken boiler is an emergency in two scenarios. First, a broken boiler is an emergency during cold weather, especially if it is the only source of heat for your home. Without heat and hot water, it will quickly become uncomfortable and difficult to live in your home. Second, a broken boiler is an emergency if the breakdown is causing a natural gas or carbon monoxide leak in the home. Leaking natural gas presents an explosion hazard, while an unstopped carbon monoxide leak can prove to be fatal to the home’s occupants.

However, a broken boiler is not an emergency during the warmer months, especially when there’s no gas or carbon monoxide leak.

It is important to take immediate action If you suspect that your boiler is broken or malfunctioning, whether the breakdown classifies as an emergency or not. You should contact a licensed and qualified technician as soon as possible to diagnose and repair the issue. If you have a gas boiler and you smell gas, you should immediately evacuate the house and call the gas emergency number.

How long can you be left without a working boiler?

The longest you can be left without a working boiler is 24 hours. Under the UK Landlord and Tenant act 1985, your council or housing association has a duty to repair or replace a malfunctioning boiler within 24 hours of being notified of the issue. The exception to this rule is if the tenant damaged the boiler intentionally or by way of negligence.

If you don’t live in council housing or in a housing association, there are no actual rules about how long you can be left without a working boiler. However, it is recommended that you have the problem addressed as soon as possible to prevent damage to your home, and so that you don’t have to live without heat or hot water for an extended period.