Boiler Not Working? 12+ Causes And Top Solutions

Last Updated on February 11, 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).

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 one of the most common reasons for poor boiler performance and can prevent your system from working altogether. When pressure is too low, it reduces water flow, making it impossible for the boiler to heat water effectively for your heating needs.

This can trigger an error code and, in some cases, cause the boiler to shut down to avoid damage.

• Leaks – Any leak in the boiler or heating system can cause pressure loss.
• Loss of Water – If the system loses water due to a leak or during routine maintenance, the pressure drops.
• Air in the System – Air trapped in the boiler or pipework can lead to pressure loss.
• Faulty Pressure Relief Valve – A malfunctioning valve can cause pressure problems that affect your boiler.

Operating your boiler at low pressure for extended periods can cause corrosion, damage to seals and pipes, and may lead to inefficient combustion, producing dangerous carbon monoxide (CO) gas.

How to Fix Low Boiler Pressure

✅ Step 1: Check the Pressure Gauge
Boiler pressure should typically be:

• 1.5 to 2 bar when the heating is on.
• 1 to 1.5 bar when the heating is off.

If the pressure is below the recommended range, you’ll need to repressurize your system.

✅ Step 2: Repressurize the Boiler
1️⃣ Turn off the boiler and allow it to cool down.
2️⃣ Locate the filling loop – A flexible hose connecting your boiler to the cold water supply.
3️⃣ Open the valves slowly to allow water into the system. Keep an eye on the pressure gauge.
4️⃣ When the pressure reaches 1.5 bar, close the valves and remove the filling loop.
5️⃣ Turn the boiler back on and check that it’s operating normally.

✅ Step 3: Call a Heating Engineer if Necessary
If you still experience low pressure after repressurising, there may be an underlying issue like a leak or faulty component. In such cases, it’s best to call a Gas Safe engineer.

Preventing Low Boiler Pressure

✔ Regularly check the pressure to ensure it’s within the optimal range.
✔ Insulate pipes to prevent damage from freezing.
✔ Schedule annual servicing to catch leaks or component issues early.

By keeping your boiler pressure at the right level, you’ll avoid performance issues and maintain a safe, efficient heating system.

8. High Boiler Pressure

High boiler pressure is a serious issue that should never be ignored. In severe cases, it can cause the boiler to rupture, leading to significant damage. If the pressure exceeds 2.75 bar, the needle on a traditional boiler pressure gauge will enter the red zone, indicating dangerously high pressure.

Why Does High Boiler Pressure Happen?

• Excessive Water in the System – Too much water in the heating system can push pressure up.
• Faulty Expansion Vessel – This component absorbs excess pressure in the system. If it malfunctions, pressure can build up.
• Thermostat Problems – If the thermostat is faulty, it may cause the system to overheat, raising the pressure.
• Faulty Pressure Relief Valve – A broken or damaged pressure relief valve may fail to release excess pressure, leading to higher levels.

Consequences of High Boiler Pressure:

• Leaks and cracks in pipes and the boiler unit.
• Increased energy waste and inefficient heating.
• Boiler damage leading to costly repairs.
• Rupturing of the boiler if pressure isn’t managed.

How to Fix High Boiler Pressure

✅ Step 1: Bleed the Radiators
Bleeding your radiators can help release air and lower the system’s pressure. Here’s how:

1️⃣ Turn off the boiler and allow the central heating system to cool down.
2️⃣ Start with the radiator furthest from the boiler. Use a radiator key or flat-head screwdriver to open the valve slightly.
3️⃣ Have a towel or bowl ready to catch any water that might escape. Once water starts to flow steadily, close the valve.
4️⃣ Move on to the next radiator, repeating the process until all radiators are bled.
5️⃣ After completing this, check the pressure gauge. It should be between 1 and 1.5 bars.

✅ Step 2: Check Pressure Relief Valve
If bleeding the radiators doesn’t resolve the issue, check the pressure relief valve. This valve releases excess pressure, so if it’s damaged or faulty, pressure may not drop to the safe range.

• A damaged valve often produces unusual sounds, like hissing, popping, or whistling.
• If the valve is faulty, it may need to be replaced by a Gas Safe engineer.

✅ Step 3: Add Water if Necessary
If the radiator bleed lowers the pressure below 1 bar, you may need to add water using the filling loop to return the pressure to the optimal level.

Preventing High Boiler Pressure

✔ Regularly check the pressure gauge to ensure pressure stays within the normal range (1.5 bar).
✔ Inspect the pressure relief valve regularly to ensure it’s in good condition.
✔ Schedule annual servicing to catch any early signs of faults with the expansion vessel or thermostat.

By addressing high pressure early, you can avoid damage and keep your boiler running efficiently.

9. Diverter Valve Problem

If you find that you have central heating but no hot water, or hot water but no heating, you’re likely facing a stuck diverter valve issue.

What is the Diverter Valve?

The diverter valve is a key component in a combi boiler, responsible for directing the flow of hot water to either the central heating or hot water system. Depending on your needs, the valve switches between heating your radiators and supplying hot water for showers, taps, or baths.

A properly working diverter valve ensures you can enjoy both a warm home and a hot shower from the same compact boiler unit.

Why Does the Diverter Valve Get Stuck?

A faulty diverter valve can’t efficiently switch between heating and hot water modes. As a result, the diverter valve can become stuck in one mode, leaving you with either:

• No hot water but functioning heating, or
• No heating but hot water.

This issue does not occur in conventional heat-only boilers, which store hot water in a separate cylinder.

Common Causes of Diverter Valve Issues

• Worn-out internal cartridge: The internal component of the diverter valve might be damaged or clogged, making it unable to switch between modes.
• Limescale buildup: In areas with hard water, mineral deposits can block the diverter valve, causing it to fail.

Solutions

✅ Step 1: Call a Professional
Replacing or repairing a diverter valve or its internal cartridge is a job for a qualified heating engineer. Due to the involvement of gas and water pipes, it’s crucial that only a professional carries out the repair to ensure safety and proper functioning.

Preventive Tips

• Regular boiler maintenance can help prevent diverter valve problems by identifying wear and tear early.
• Consider installing a water softener if you live in an area with hard water to reduce limescale buildup.

If your diverter valve is malfunctioning, it’s best to get it fixed promptly to avoid prolonged discomfort with your heating and hot water supply.

10. Printed Circuit Board Malfunction

The Printed Circuit Board (PCB) is the brain of your boiler. It controls all the critical functions of the system, ensuring it operates smoothly and efficiently. If the PCB malfunctions, it can lead to a range of issues, from minor disruptions to complete boiler failure.

Signs of a Malfunctioning PCB:

• No power or display on the boiler panel.
• Erratic or intermittent operation of the boiler.
• A burning smell or visible smoke coming from the boiler.
• Boiler displaying error codes or entering a lockout state.
• Loss of heating or hot water.

What Causes PCB Failure?

A malfunctioning PCB can be caused by several factors:

• Electrical faults: Power surges or short circuits can damage the PCB.
• Wear and tear: Over time, components on the PCB can degrade.
• Water damage: Leaks in the system or moisture intrusion can lead to PCB issues.
• Poor installation or wiring: Incorrect installation can put stress on the PCB, leading to malfunctions.

Solutions

Call a Professional
Due to the complexity and sensitivity of the PCB, it’s best to have a qualified heating engineer handle the diagnosis and repair. If the PCB is faulty, a replacement is often necessary.

Repair or Replacement
While repairing the PCB may be possible in some cases, a replacement is usually the more reliable option. The process involves removing the old PCB and installing a new one, which may require recalibration and testing to ensure proper functionality.

Cost Consideration
The cost of replacing a PCB, including installation, can be upwards of £500. Depending on the age and condition of your boiler, you may also want to consider investing in a new boiler, especially if the cost of repairs is approaching or exceeding the value of the unit.

Preventive Tips

• Ensure regular maintenance to catch early signs of PCB issues before they escalate.
• Avoid sudden power surges by using surge protectors for your boiler’s power supply.

If your boiler is experiencing any of the symptoms listed above, contact a professional right away to avoid further damage or costly repairs.

11. Damaged Heat Exchanger

The heat exchanger is a critical component in gas and oil boilers, responsible for transferring heat from the fuel combustion process to the water circulating in the boiler. If the heat exchanger is malfunctioning, it directly affects the boiler’s performance and efficiency.

What Causes Damage to the Heat Exchanger?

Over time, the heat exchanger can become clogged or damaged due to several factors:

• Sludge buildup: This occurs when debris accumulates in the system, restricting water flow and heat transfer.
• Limescale formation: In hard water areas, minerals can deposit on the heat exchanger, reducing its effectiveness.
• Lack of maintenance: Regular maintenance helps prevent these issues and ensures optimal functioning.

Signs of a Damaged Heat Exchanger:

• Loss of heating or hot water: If the heat exchanger isn’t transferring heat properly, you’ll notice a lack of hot water or heating.
• Leaking water or steam: Water or steam leaking from the boiler or pipes can indicate a cracked or corroded heat exchanger.
• Banging, clanging, or hissing noises: These boiler noises often occur when sludge or limescale buildup blocks the system.
• Higher energy bills: A damaged heat exchanger can make your boiler inefficient, leading to increased energy consumption.
• Carbon monoxide (CO) risk: If the heat exchanger is damaged, dangerous gases, like carbon monoxide, might escape into your home.

Solutions

✅ Step 1: Power Flushing or Descaling
Sludge and limescale buildup can often be treated through power flushing or descaling. This process removes debris and mineral deposits, restoring the heat exchanger’s efficiency. It’s a specialized task and should be handled by a professional.

✅ Step 2: Replacement
If your heat exchanger is severely damaged, corroded, or cracked, replacement is typically the only solution. The cost of replacing a heat exchanger can range from £400 to £1,000+, depending on the severity of the damage and the type of boiler.

In some cases, especially if the boiler is older, it may be more cost-effective to invest in a new boiler rather than replacing just the heat exchanger.

Risks of Ignoring a Faulty Heat Exchanger

Ignoring the issue can lead to more expensive repairs or safety risks such as carbon monoxide poisoning, which is extremely dangerous. Regular maintenance and prompt repairs are essential to ensuring your boiler remains safe and efficient.

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.

Is It Time for a New Boiler?

Over time, boiler repairs can add up, leaving you with mounting costs and frequent service visits. If you’ve found yourself facing recurring issues or expensive repairs, it might be more cost-effective in the long run to invest in a new boiler.

At Eco Happy, we believe in helping you make the best decision for your home and budget. While occasional repairs are normal, ongoing issues may signal that your boiler is nearing the end of its life.

A new, more efficient boiler could save you money on energy bills, reduce maintenance costs, and provide peace of mind knowing you’re investing in a reliable system.

Ready to find out if a new boiler is the right move for you? Request a free quote today! It’s simple—just answer a few quick questions, and we’ll provide you with a personalised quote that’s perfect for your home.

We’ll get back to you within minutes with the best options tailored to your needs. Don’t wait—take the first step toward a more efficient home today!

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.