How to Safely Reset Your Boiler & Understand Fault Codes

By The FixDelivered Team · Updated 2026-07-05 · 7 min read

A cold house and no hot water are never welcome, especially when your boiler displays an unfamiliar fault code. While it can be tempting to panic, understanding how to safely reset your boiler and what those codes might mean can often save you time and discomfort. This guide will walk you through the essential steps for a safe reset and help you decipher those cryptic messages, always prioritising your safety and advising when to call a qualified professional.

Before You Reset Your Boiler

Before you press that reset button, it's crucial to perform a few quick checks. This can often resolve the issue without needing a reset or prevent a reset from being a temporary fix for a deeper problem.

Check Your Power Supply: Ensure the boiler is plugged in and the fuse spur (often a switch near the boiler) is on. Check your consumer unit (fuse box) for any tripped circuit breakers.
Check Your Gas Supply: Make sure your gas meter's isolation valve is open and that other gas appliances (like your hob) are working. If you smell gas, turn off the supply immediately, open windows, and call your gas network emergency number – do NOT attempt to reset your boiler or use any electrical appliances.
Check Your Thermostat: Is your room thermostat set to a temperature higher than the current room temperature? Is it programmed correctly? Are the batteries flat if it's wireless?
Check Your Boiler Pressure: Most boilers have a pressure gauge, usually with a green zone. It should typically be between 1.0 and 1.5 bar when the system is cold. If it's too low, you might need to repressurise your boiler (see instructions below) before attempting a reset.

How to Safely Reset Your Boiler

If the preliminary checks haven't resolved the issue, a reset can sometimes clear a temporary glitch. Always consult your boiler's instruction manual first, as reset procedures can vary slightly between models and manufacturers.

Locate the Reset Button: This is usually clearly labelled on the front control panel of your boiler. It might be a button marked 'Reset', 'R', or a symbol resembling a flame with a cross through it. Some newer digital boilers might have a menu option for resetting.
Press and Hold: For most boilers, you'll need to press and hold the reset button for a few seconds (typically 3-5 seconds). Do not hold it down for an extended period.
Release and Wait: Release the button and wait. The boiler will typically go through a restart sequence, which may involve whirring, clicking, and flashing lights. This can take a few minutes.
Observe: See if the boiler fires up and begins to operate normally. Check if the fault code has cleared and if you have heat and hot water.

When to Call a Professional After a Reset

If your boiler repeatedly displays the same fault code after a reset, or if it fails to restart, it's a clear sign of an underlying issue that requires professional attention. Do not attempt multiple resets as this can sometimes exacerbate the problem or indicate a serious fault.

Understanding Boiler Fault Codes

Boiler fault codes are diagnostic messages displayed by your boiler's internal computer system. They are designed to help Gas Safe registered plumbers quickly identify the nature of a problem. While the specific codes vary significantly by manufacturer (e.g., Worcester Bosch, Vaillant, Baxi, Ideal), they generally point to categories of issues.

Common Categories of Boiler Fault Codes

Low Pressure: Often indicated by codes like 'F.22', 'F.75', 'E.118'. This is a very common issue and often one you can fix yourself by repressurising the system (see below).
Ignition Lockout: Codes such as 'E.28', 'F.28', 'A.29' typically mean the boiler tried to ignite but failed. This could be due to a temporary gas supply interruption, a faulty igniter, or a blocked flue.
Sensor Faults: Codes like 'F.20', 'F.27', 'L.2' often relate to temperature sensors or flow sensors. These require a professional diagnosis and replacement.
Overheat Protection: Codes such as 'F.1', 'F.20', 'L.1' indicate the boiler has detected an unsafe temperature and shut down as a safety measure. This is serious and needs immediate professional inspection.
Fan/Flue Issues: Codes like 'F.5', 'F.35', 'E.133' suggest a problem with the fan or the flue system, which is critical for safe operation and requires a Gas Safe engineer.
Water Leak: While less common for a direct code, a significant drop in pressure that cannot be maintained after repressurising often points to a leak in the system.

Always check your boiler's manual first. It will provide a comprehensive list of fault codes specific to your model and what action to take. If you've misplaced your manual, most manufacturers offer digital versions on their websites.

DIY: How to Repressurise Your Boiler (Low Pressure Faults)

If your fault code indicates low pressure, this is often a DIY fix. You will need your boiler manual, a towel, and possibly a small screwdriver.

Tools Needed:

Boiler manual
Towel or cloth

Safety Cautions:

Ensure the boiler is switched off and cool before attempting this.
Do not over-pressurise the system.
If you are unsure at any point, stop and call a professional.

Step-by-Step Instructions:

Switch Off the Boiler: Turn off both the electrical supply and the gas supply to the boiler. Allow it to cool down completely.
Locate the Filling Loop: This is typically a silver braided hose with two valves at either end, usually found underneath your boiler. Some boilers have an internal filling key/mechanism. Consult your manual to locate it.
Connect/Open Valves: If it's an external filling loop, ensure both ends are securely connected. If internal, engage the key/lever as per your manual. Slowly open one of the valves on the filling loop, and then slowly open the second. You should hear water entering the system.
Monitor the Pressure Gauge: Watch the boiler's pressure gauge carefully. It should rise steadily. For most domestic systems, you want to reach between 1.0 and 1.5 bar (check your manual for the exact recommended pressure).
Close the Valves: Once the desired pressure is reached, close BOTH valves on the filling loop, one after the other, ensuring they are fully shut.
Disconnect (if external): If you have an external filling loop, disconnect it and store it safely. You may get a small amount of water drip out, which is normal.
Restart the Boiler: Turn the electrical and gas supply back on to your boiler. Press the reset button if necessary.
Check for Leaks: Keep an eye on the pressure gauge over the next few hours and days. If the pressure drops again quickly, you likely have a leak in your system, which needs professional attention.

When to Call a Professional:

If you cannot locate the filling loop or are unsure how to use it.
If the pressure doesn't rise, or rises too quickly.
If the pressure drops again shortly after repressurising, indicating a leak.
If you have to repressurise your boiler frequently (more than once every few months).

When to Call a Professional Plumber

While a simple reset or repressurisation can solve minor issues, many boiler problems require the expertise of a Gas Safe registered engineer. Never attempt to open your boiler's casing or tamper with internal components yourself. It's dangerous and could invalidate your warranty.

You should call a professional if:

Your boiler repeatedly displays the same fault code after a reset.
You smell gas – turn off the supply and call your gas network emergency line immediately.
There are visible water leaks from the boiler or pipework.
The boiler is making unusual noises (banging, gurgling, whistling).
The pilot light keeps going out (if your boiler has one).
There is no heat or hot water, even without a fault code.
You are unsure about any step of the diagnostic or repair process.

Typically, a plumber's call-out fee for an emergency boiler issue in the UK can range from £80-£150, with repairs potentially adding £150-£400+ depending on the complexity and parts needed. These are rough 2026 guides and can vary by region and time of day.

If you're facing a persistent boiler issue and need a trusted expert, FixDelivered can connect you with emergency plumbers near you quickly. Our vetted professionals are all Gas Safe registered plumbers, ensuring your safety and peace of mind. You can learn more about how FixDelivered works and find a local plumber when you need one.

Don't let a boiler breakdown leave you in the cold. Knowing these steps can help you manage the situation effectively and safely.

Frequently asked questions

What does it mean if my boiler keeps tripping or resetting?

If your boiler frequently trips or requires resetting, it indicates an underlying issue that needs professional investigation. Do not continually reset it; instead, call a Gas Safe registered engineer to diagnose the fault.

Can I fix a boiler fault code myself?

Some minor issues, like low pressure, can often be resolved by following your boiler's repressurisation instructions. However, most fault codes indicate internal component failures or safety issues that require a qualified Gas Safe registered engineer to diagnose and repair.

How much does it cost to get a plumber to fix a boiler fault?

As a rough guide for 2026, a plumber's call-out fee for a boiler fault typically ranges from £80 to £150. The total cost for repair will depend on the diagnosis, parts required, and labour time, often ranging from £200 to £400+ for common repairs, excluding major component replacements.

Is it safe to reset my boiler if I smell gas?

Absolutely NOT. If you smell gas, turn off your gas supply at the meter, open windows and doors, and immediately call your gas network emergency number. Do not attempt to reset your boiler or use any electrical appliances.

Need a plumber now? Tell us your emergency and FixDelivered will find and confirm an available local plumber near you, usually within the hour.

Written by the FixDelivered Team. Reviewed by Rupert Lowe, Editor. Last updated 2026-07-05.