Boiler Not Working? 12+ Causes And Top Solutions

Last Updated on February 4, 2025

A faulty boiler can be frustrating, especially during colder months. Issues can range from frozen condensate pipes and low boiler pressure to faulty components or even a gas supply interruption.

In this comprehensive guide, we’ll walk you through 12+ common reasons why your boiler isn’t working and provide practical solutions to get it running again.

The good news? Many boiler problems have simple fixes you can do yourself—without calling a Gas Safe registered engineer. However, for more complex issues, professional help may be necessary.

Let’s dive into the most common boiler faults and how to troubleshoot them effectively.

1. The Boiler Is Switched Off

Before diving into complex boiler issues, check if your boiler is turned on—you’d be surprised how often this is the cause of a “broken” boiler! Many homeowners experience an unexpected boiler shutdown due to:

• A power cut – Local outages can switch off your boiler, disrupting its settings.
• A manual shutdown – It may have been turned off for maintenance, repairs, or to thaw a frozen condensate pipe.

Solution: Restart Your Boiler

If your boiler isn’t firing up, a simple reset can often resolve the issue. Similar to rebooting a computer, a reset clears minor faults or glitches.

✅ How to reset your boiler:

• Locate the reset button on the front control panel (refer to your boiler manual if needed).
• Press and hold the reset button for a few seconds.
• Wait for the boiler to restart.

If a reset doesn’t work, try switching the boiler off and on again at the mains.

⚠️ Frequent boiler resets? If you’re resetting your boiler regularly, it may indicate an underlying issue. In this case, contact a Gas Safe registered engineer to diagnose and fix the problem.

2. Power Supply Problems

Your boiler won’t work without electricity, even if it runs on gas, LPG, or oil. Most modern boilers rely on electricity for ignition, thermostats, and control systems. If your boiler isn’t turning on, a power supply issue could be the culprit.

Common Causes of Boiler Power Failure:

Power cut – If there’s an outage in your area, your boiler will remain off until electricity is restored.
Tripped circuit breaker or blown fuse – A power surge can trip your fuse box, cutting off electricity to your boiler.
Loose wiring or faulty switch – A damaged power switch or internal wiring issue could be preventing the boiler from powering up.

Solutions: How to Restore Power to Your Boiler

✅ Step 1: Check for a Power Cut

• Look outside or ask your neighbours if they also lost power.
• If it’s a local outage, your electricity provider should restore service soon.

✅ Step 2: Inspect Your Fuse Box

• Check if any circuit breakers have tripped. If so, reset the switch.
• If a fuse has blown, replace it with one of the same rating.

✅ Step 3: Examine Your Boiler

• Look for loose wires, a faulty switch, or visible damage.
• If you spot an issue, call a Gas Safe registered engineer for repairs.

✅ Step 4: Reset Your Boiler

• Once power is restored, reset your boiler by pressing the reset button on the control panel.

If your boiler still won’t start after a power outage, it could indicate a deeper electrical fault—consult a professional for further diagnosis.

3. Gas Supply Problems

If your boiler isn’t igniting, a gas supply issue could be the cause. Several factors can disrupt the gas flow to your boiler, preventing it from functioning properly.

Common Causes of Gas Supply Issues:

Gas supply shutdown – Your gas supplier may have temporarily shut off service due to an emergency.
Low gas pressure – A drop in pressure can prevent your boiler from igniting.
Frozen gas meter – In cold weather, a frozen gas meter can obstruct gas flow to the boiler.
Contaminated gas supply – If the gas pipe or filter is improperly installed, air and impurities may prevent proper combustion.
Faulty gas valve – A malfunctioning valve may restrict gas flow, stopping the boiler from working.

Solutions: How to Fix Gas Supply Issues

✅ Step 1: Check If Your Gas Supply Is Turned Off

• Ensure you haven’t accidentally turned off the gas isolation valve.

✅ Step 2: Test Other Gas Appliances

• Try using your gas stove or another gas appliance.
• If none work, contact your gas supplier to check for service disruptions.

✅ Step 3: Inspect Your Gas Meter

• Look for visible damage to the meter.
• If it’s frozen, carefully thaw it with warm (not boiling) water or wrap it with a hot towel.
• Prevent future freezing by insulating (lagging) the meter.

✅ Step 4: Call a Gas Safe Engineer

• If the issue persists, a professional can check the gas valve and ensure your boiler is properly installed.

⚠️ Safety Warning: Never attempt DIY gas repairs—always seek help from a Gas Safe registered engineer.

4. Thermostat Down

Your thermostat is the control center of your heating system, managing temperatures, schedules, and remote settings via apps. If the thermostat fails to signal your boiler to turn on, your heating won’t function properly.

Common Thermostat Problems:

Flat batteries – If your thermostat runs on batteries, it may need a replacement.
No power supply – A wired thermostat may have a faulty connection.
Wi-Fi issues – Smart thermostats need a stable Wi-Fi connection to communicate with the boiler.
Faulty thermostat – If the thermostat is damaged, it won’t regulate heating correctly.
Poor thermostat placement – If placed near a radiator or fireplace, it may misread room temperature and cause short cycling (frequent on/off cycling).

Solutions: How to Fix Thermostat Problems

✅ Step 1: Check Power & Batteries

• Replace batteries if your thermostat runs on them.
• Ensure wired thermostats are properly connected to power.

✅ Step 2: Check Wi-Fi & Settings

• Restart your router if your Wi-Fi thermostat isn’t connecting.
• Ensure your thermostat isn’t in holiday mode or standby mode.

✅ Step 3: Optimize Thermostat Placement

• Keep it away from direct heat sources (radiators, fireplaces, or direct sunlight).
• Place it in a central room to ensure accurate temperature readings.

✅ Step 4: Repair or Replace If Faulty

• If your thermostat remains unresponsive, a heating technician may need to repair or replace it.

By ensuring your thermostat is powered, correctly placed, and properly configured, you can prevent boiler heating issues and optimize energy efficiency..

5. Frozen Condensate Pipe

The condensate pipe removes wastewater from your boiler and directs it outside. However, in freezing temperatures, the water inside this pipe can freeze and block the flow, triggering an error message and potentially shutting down your boiler.

How to Identify a Frozen Condensate Pipe

• Your boiler displays an error code or stops working.
• You see ice or frost on an external pipe leading from your boiler.
• You hear gurgling noises, indicating trapped water.

How to Thaw a Frozen Condensate Pipe

✅ Step 1: Turn Off Your Boiler
Switch off the boiler at its control panel to avoid damage.

✅ Step 2: Locate the Frozen Section
Find the external condensate pipe—usually a white or black plastic pipe leading from your boiler to an outside drain. Look for frost or ice buildup.

✅ Step 3: Gently Thaw the Pipe

• Pour warm (not boiling) water over the frozen section.
• Wrap the pipe with hot towels or press a hot water bottle against it.

✅ Step 4: Restart Your Boiler
Once the pipe is fully thawed, switch your boiler back on and reset it.

How to Prevent a Frozen Condensate Pipe in Winter

• Insulate the pipe with lagging to reduce freezing risk.
• Check the pipe regularly and remove snow or ice buildup.
• If the pipe freezes often, consider rerouting it indoors or increasing its diameter to improve drainage.

By proactively protecting your condensate pipe, you can prevent boiler breakdowns and keep your heating system running smoothly during winter.

6. Pilot Light Not Burning Bright

While modern boilers use electronic ignition, older gas boilers rely on a pilot light—a small flame that ignites the main burner. If the pilot light goes out, the boiler won’t heat your home.

Why Does the Pilot Light Go Out?

• Draughts – A strong gust of air can extinguish the flame.
• Faulty Thermocouple – This safety device detects heat from the pilot light. If it’s dirty or broken, it may shut off the gas supply.
• Gas Valve Issues – A faulty valve can prevent gas from reaching the burner.
• Low Gas Pressure – Insufficient gas flow may cause the flame to flicker out.

How to Fix a Pilot Light That Won’t Stay Lit

✅ Step 1: Check for a Gas Supply Issue

• Ensure your gas meter is working.
• Check if other gas appliances are functioning.
  
  ✅ Step 2: Relight the Pilot Light (Refer to your boiler manual for exact steps)
• Turn off the boiler and wait at least 5 minutes for gas to clear.
• Locate the pilot light assembly and find the reset button.
• Press and hold the reset button while using a long lighter or ignition switch to relight the flame.
• Keep the button pressed for 30-60 seconds, then release.

✅ Step 3: Call a Gas Safe Engineer If Needed
⚠️ DO NOT attempt to replace the thermocouple or gas valve yourself. These are Gas Safe engineer-only repairs.

Preventing Pilot Light Issues

• Keep the area free of draughts to prevent extinguishing the flame.
• Schedule regular boiler servicing to maintain the thermocouple and gas valve.
• Check for low gas pressure—if it’s a recurring issue, call your supplier.

By troubleshooting the pilot light properly, you can avoid unnecessary callouts and ensure efficient heating. However, if problems persist, a Gas Safe engineer should assess your system.

7. Low Boiler Pressure

Low boiler pressure is a major cause of poor performance and can result in a boiler not working. When the pressure is too low, water flow is reduced and the boiler cannot heat enough water to serve the central heating needs. Expect an error code and possibly the boiler to shut down to prevent damage.

Operating at low pressure often or for long periods puts strain on seals, pipes and fittings, and contributes to corrosion. Sometimes, low pressure is caused by leaks in the boiler or heating system. It, in turn, can cause further leaks.

Low boiler pressure can also lead to inefficient combustion in the boiler, potentially producing dangerous carbon monoxide (CO) gas.

Solutions

Boiler pressure should be between around 1.5 and 2 bar when the heating is on and between 1 and 1.5 bar when the boiler is off. Check your pressure gauge or digital display. If the pressure is below these levels, you need to increase it by adding more water to the system. You do this by using the filling loop – a flexible hose connecting the boiler to the cold water pipe. Follow these steps:

1. Turn off the boiler and wait for it to cool down.
2. Locate the filling loop which will have one or possibly two valves that you should open.
3. Open the valves slowly and keep an eye on your pressure gauge. Listen out to hear water filling the system.
4. When the pressure increases to the required level (between 1 and 1.5 bar), close the valves and remove the filling loop.
5. Turn on the boiler and see that it works normally.

Repressurising your boiler is normally something you can do yourself if you’re comfortable with the process. There is no need to call a Gas Safe engineer or heating plumber.

If the low pressure is caused by a leak or a broken component, you should call an engineer out. A small leak repair that is easily accessible is not too expensive. Expect the cost to mount if the leak is under the floorboards.

8. High Boiler Pressure

High pressure is another problem that should never be ignored. In extreme cases, it can lead to the boiler rupturing.

High boiler pressure means the pressure is heading to 2.75 bar and over. A traditional boiler pressure gauge will show the needle in the red zone – a clear warning sign. Regular or continual high pressure damages the boiler’s parts and wastes energy. Consequences include leaks and cracks in the unit or pipes and increased running boiler repairs.

The problem is worsened if the boiler’s pressure relief valve is damaged. The pressure relief valve is a critical safety device that releases excess pressure by letting water and steam out of the system to prevent leaks and rupturing.

A damaged valve often makes unusual sounds such as hissing, popping, or whistling. If this safety valve is faulty and unable to lower the pressure, the entire heating system may shut off.

Solutions

The usual first fix for high pressure is to bleed the radiators. Bleeding your radiators lowers the pressure by releasing air and some water from the system. Here’s how to bleed your radiators:

1. Turn off the boiler and wait for your central heating system to cool down.
2. Start with the radiator furthest from the boiler and use a radiator key or flat-head screwdriver to open the valve slightly.
3. Have a bowl or towel ready to catch the water that comes out of the valve. Once water rises and exits the valve, close it and move on to the next radiator.
4. After bleeding all your radiators, check that the pressure gauge shows between 1 and 1.5 bars. If it is too low, you may need to add some water using the filling loop.

If a radiator bleed doesn’t resolve the problem, you’ll want a professional to check that the relief valve isn’t damaged, loose, or leaking.

9. Diverter Valve Problem

Do you have central heating but no hot water? Or hot water but no heating? This sounds like the classic stuck diverter valve problem.

The diverter valve is the switching mechanism in a combi boiler that directs the flow of hot water to different parts of the central heating system, depending on demand. A working diverter valve ensures that you enjoy both a warm shower and toasty radiators from one compact combi unit.

A problem arises when a faulty valve can’t divert heat efficiently or gets stuck in either heating or hot water mode. The result is that you sit without hot water or radiator heat, depending on how it is stuck.

This is obviously not a problem in conventional heat-only boilers that store hot water in a separate cylinder.

Solutions

You may well need to replace the diverter valve or the cartridge inside it. This is not a simple DIY job as it involves working with gas and water pipes. It’s best to call in a qualified heating engineer or plumber/electrician.

10. Printed Circuit Board Malfunction

The Printed Circuit Board (PCB) is the boiler’s central control unit. It is the brain that drives and regulates the boiler’s safe, effective functioning. A malfunctioning PCB will throw up all kinds of grief, including:

• No power or display on the boiler panel.
• Intermittent or erratic operation.
• A burning smell or smoke from the boiler.
• Boiler error codes; boiler lockout.
• Loss of heating or hot water.

Solutions

It may be possible to repair your boiler PCB but more often than not a replacement is needed. Replacing a PCB requires professional installation and testing due to its sensitivity and critical function. Depending on model and make, the cost of replacement and installation can easily exceed £500.

In some cases, it’s worth considering investing in a new boiler instead, especially if your boiler is out of warranty and has been giving you problems over and above the PCB issue.

11. Damaged Heat Exchanger

Gas and oil boilers feature a heat exchanger. This is the system that transfers the heat produced by burning fuel (gas, oil, LPG) to the water circulating within the boiler. The heat exchanger is a highly critical component in the process. If it’s not operating as it should, the system suffers.

The heat exchanger will accumulate debris or sludge over time if not well maintained. Limescale also builds up on the heat exchanger, especially in hard water areas. Banging or whistling noises are usually telltale signs that your exchanger is clogged up.

Common consequences of a bad exchanger are:

• Loss of heating or hot water.
• Leaking water or steam from the boiler or pipes.
• Banging, clanging, or hissing boiler noises.
• Higher energy bills due to inefficient heat delivery.
• There is even a risk of carbon monoxide (CO) poisoning. A working heat exchanger contains the combustion gases, including carbon monoxide, and vents them out of the home via the flue. A damaged heat exchanger may allow carbon monoxide to escape into the house.

Solutions

• Sludge and limescale buildup on a heat exchanger can be fixed by power flushing the system or descaling the boiler. It’s best to leave these flushes to an expert.
• When your heat exchanger is badly damaged, corroded, or cracked, replacement is usually the only option. This isn’t cheap and the cost generally ranges from £400 to over £1,000 with installation. Here, you may need to think about a brand-new boiler rather than simply a new part.

12. Other Key Boiler Components

Besides the heat exchanger, the following major components will also seriously compromise performance if they are damaged or faulty.

• Burner: The burner ignites the fuel to generate heat in the boiler. A problematic burner means your boiler is not firing on all cylinders.
• Pump: The pump circulates water throughout the system. Expect cold spots and poor heating if the pump isn’t doing its job. A bad pump may make grinding or vibrating noises.
• Motor: The motor powers the pump and other moving components and ensures the boiler’s smooth functioning. A bad motor which may also make grinding noises could shut down the pump and other working parts.
• Expansion vessel: The expansion vessel absorbs excess pressure in the system, preventing damage due to pressure strain. When this safety vessel isn’t working, excessive pressure may build up placing tremendous strain on the entire setup.

Replacement of any of these parts will cost a few hundred pounds (over £500 for a burner) and installation should be handled by someone certified.

FAQs

Can trapped air cause my boiler to stop working?

Trapped air in a boiler system can lead to complications such as reduced heating efficiency, uneven heating in radiators, gurgling or banging noises, and unhealthy fluctuations in pressure. While trapped air doesn’t usually shut down the boiler, it will negatively affect the overall performance of the central heating system if not addressed. Bleeding the radiators is the go-to solution to release air.

How can I prevent common boiler problems in the future?

Regular boiler maintenance – such as annual servicing by a qualified technician, bleeding radiators to remove trapped air, avoiding a blockage of your condensate pipe, and monitoring and managing your boiler’s pressure – will help avoid common issues and deliver a happy heating experience.

What could be causing my boiler to short cycle?

Short cycling refers to the boiler turning on and off frequently and rapidly. Short cycling may result from a faulty thermostat, inadequate water flow, or a damaged pressure sensor. Have a technician inspect the affected components and repair them if necessary.

Conclusion

You will appreciate that there are numerous potential boiler problems, and just as many ways to resolve them. Some fixes are simple (yes, as simple as turning the boiler back on!). Familiarising yourself with your boiler manual and boiler error codes is always a good idea. Some problems involve a complex assessment of crucial parts by a Gas Safe registered engineer or a certified electrician.

You may be faced with a pricey decision. Do I replace my heat exchanger or should I invest in a new boiler? Getting advice from your engineer and other heating experts is key. If you need personalised guidance or quotes, Eco Happy is here to help. Contact Eco Happy to chat about solutions that are right for you.