Boiler Not Firing Up? Common Causes & Fixes

Your home’s comfort quickly fades when your boiler fails to fire up. Whether your central heating isn’t turning on, your hot water isn’t working, or both have suddenly stopped, the disruption is always inconvenient, especially during colder months.

If your boiler is not firing up, take a deep breath. You’re not alone, and in many cases, the cause is minor and fixable. At 24|7 Home Rescue, we understand how stressful boiler issues can be. That’s why we’ve created this detailed guide. Our goal is to empower you to identify what’s gone wrong, how you can attempt to resolve it safely, and when it’s time to call a professional.

This guide outlines the most common reasons your boiler may not fire up, along with error codes associated with top boiler brands, so you know exactly what to expect.

Common Reasons Why Your Boiler Is Not Firing Up (With Brand Error Codes)

1. No Gas Supply or Ignition Failure

One of the most common reasons a boiler fails to ignite is a gas supply problem or an ignition fault. If no gas reaches the boiler or the burner fails to ignite, your heating system will shut down for safety.

What to check:

• Turn on another gas appliance, such as your hob, to ensure the gas supply works.
• If you have a prepayment meter, check for enough credit.
• Make sure the gas shut-off valve is open.
• Reset the boiler to see if the ignition restarts.

If these checks do not resolve the issue, a fault with the ignition system, spark electrode, or gas valve may be present.

Relevant error codes:

• Worcester Bosch: EA – No flame detected
• Vaillant: F28 – Ignition failure, F29 – Flame extinguished
• Baxi: E133 – Ignition fault or no gas supply
• Ideal: L2 – Ignition lockout
• Glow-worm: F28 – No flame or ignition fault

Call a Gas Safe engineer if your boiler displays one of these codes and won’t reset.

2. Low Water Pressure

Domestic boilers require a minimum water pressure (typically between 1.0 and 1.5 bar) to function. If the system pressure is too low, the boiler may not fire up to prevent damage.

What to check:

• Look at the pressure gauge on your boiler.
• If the reading is below 1.0 bar, repressurising the boiler using the filling loop may solve the problem.
• If you repressurise it and the pressure drops again, there may be a leak or an issue with the pressure relief valve.

Relevant error codes:

• Ideal: F1 – Low water pressure
• Baxi: E119 – Low pressure
• Glow-worm: F22 – Low system pressure

Consistently low pressure may indicate a hidden leak and require professional inspection.

Related Article: How to increase boiler pressure?

3. Frozen Condensate Pipe (Common in Winter)

In cold weather, the external condensate pipe can freeze, causing a blockage that prevents the boiler from firing up. This pipe carries wastewater from the boiler to an external drain, and when blocked, the boiler shuts down to avoid flooding or pressure build-up.

What to check:

• If your boiler stopped working during freezing temperatures, the condensate pipe may be frozen.
• Locate the pipe, usually outside, and see if it feels or looks frozen.
• Gently pour warm (not boiling) water over the pipe to thaw the blockage.
• Once cleared, reset the boiler.

Relevant error codes:

• Worcester Bosch: EA – Ignition fault due to blockage
• Vaillant: F28 / F29 – Ignition or flame loss due to condensate issue

This is a common issue during winter and can usually be resolved safely by following the manufacturer’s guidance.

Related Article: How to defrost a frozen condensate pipe

4. Faulty Thermostat or Incorrect Settings

Sometimes the problem lies with the thermostat or boiler controls. If the thermostat is not calling for heat or the settings are incorrect, your boiler may not receive the signal to ignite.

What to check:

• Ensure the thermostat is turned on and has working batteries.
• Set the temperature a few degrees higher than the current room temperature.
• Confirm that your heating schedule and timer are correctly set.
• If your home recently experienced a power cut, the timer settings may have reset.

Thermostat-related issues usually don’t trigger fault codes but can prevent the boiler from functioning altogether.

Related Article: How does a thermostat work?

5. Diverter Valve Stuck (Hot Water Works, Heating Does Not)

If you’re receiving hot water but your central heating won’t come on, the issue may lie with a stuck or faulty diverter valve. This is especially common in combi boilers.

What to check:

• Turn on your hot water tap and then the heating.
• If the boiler only fires up when the hot water tap is on, the diverter valve may be stuck in the hot water position.

A Gas Safe engineer should only inspect and repair this internal component. There is usually no error code associated with a stuck diverter valve.

Related Article: What is a boiler diverter valve?

6. Electrical Supply or PCB Fault

If your boiler is completely unresponsive, no lights, no display, it could be due to a tripped fuse, a power cut, or a fault in the Printed Circuit Board (PCB).

What to check:

• Ensure the boiler is plugged in and switched on.
• Check your fuse box for tripped switches.
• Press the boiler’s reset button.

If the display remains blank or flickers intermittently, it may be an internal electrical fault.

Relevant error codes:

• Worcester Bosch: A1 – Low pressure or power supply issue
• Vaillant: F62 – Gas valve or control fault
• Ideal: L2 – Lockout (can be linked to PCB issues)

These faults usually require diagnosis and repair by a qualified engineer.

Related Article: How to diagnose boiler PCB Faults and the cost of replacement

Troubleshooting Checklist Before Calling an Engineer

Before you request a call-out for boiler issues, please take the time to work through the following detailed checklist to troubleshoot the problem:

1. Check the Gas Supply: Make sure that the gas supply in your home is functioning properly. Confirm that the gas valve is open and there are no gas outages in your area.

2. Inspect the Boiler Pressure Gauge: Look at the pressure gauge on your boiler. The pressure should typically be between 1 and 1.5 bar when the system is cold. If the pressure is too low, you may need to repressurize the system.

3. Verify Thermostat Settings: Ensure that the thermostat is set to a temperature that is higher than the current room temperature. This will prompt the boiler to start heating.

4. Check for Frozen Pipes: In colder months, it’s important to inspect exposed pipes for any signs of freezing. Look for areas that are particularly cold, and consider applying gentle heat or insulation if necessary.

5. Try Resetting the Boiler: Most modern boilers have a reset button. Follow the manufacturer’s instructions to reset the boiler, which can sometimes resolve minor issues.

6. Review Programmer or Timer Settings: Ensure that the programmer or timer is correctly set to the desired heating schedule. Check if the settings may have been inadvertently changed.

7. Look for Error Codes: Examine the display on your boiler for any error codes or warning lights. Refer to the user manual to understand what the codes indicate and how to resolve any issues.

If, after going through these steps, your boiler still fails to ignite, or if you feel uncertain about any aspect of the process, it is advisable to contact a qualified professional for assistance. Your safety and comfort are paramount, so don’t hesitate to seek expert help.

When to Contact a Gas Safe Registered Engineer

You should contact a qualified engineer immediately if:

• The boiler displays a persistent error code and won’t reset.
• If you suspect a gas leak (in this case, call the National Gas Emergency line at 0800 111 999).
• The boiler leaks water or makes unusual noises like banging or whistling.
• There is no power to the boiler, and the issue isn’t due to a power cut or tripped fuse.
• The water pressure repeatedly drops even after repressurising.
• The diverter valve or pump may have failed.

A certified Gas Safe engineer should handle all internal boiler faults. Call us now at 0345 3192 247 or manage your claim through the 24|7 Home Rescue App for fast, convenient service.

Boiler Service

Ensure your boiler runs efficiently and safely with our professional boiler servicing. Regular maintenance will save you money in the long run and potentially prevent breakdowns.

Schedule a Boiler Service

Prevent Future Breakdowns with Boiler Cover

Boiler repairs can be costly, sometimes reaching over £1,000. With 24|7 Home Rescue, you can avoid large repair bills and reduce stress with one of our flexible boiler cover options.

We offer:

• Boiler breakdown cover
• Annual Boiler Service
• Home Emergency cover
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Visit 247HomeRescue to find a policy that suits your needs.

Conclusion

If in doubt, don’t take risks. It is illegal and unsafe for anyone not Gas Safe registered to attempt repairs on a gas appliance. Safety should always come first. For any gas-related concerns, always consult a qualified engineer.