How to Reset a Combi Boiler (General Guide)

Most modern combination (combi) boilers come equipped with safety features that activate a lockout mode when a fault is detected.

Once you’ve identified the error code and addressed the underlying issue, the next step is usually to reset the boiler to clear the fault.

However, the reset process can vary slightly depending on the boiler’s brand and model. Always refer to your boiler’s manual if you’re unsure.

But what are the common reasons that may force you to reset your combi boiler?

Common Reasons That Require A Boiler Reset

Your modern combi boiler performs a system shutdown or activates lockout mode to prevent damage or hazardous operation.

Here are the most common issues that will trigger your modern combi boiler’s lockout mode:

Ignition Failure:

According to the Ministry of Housing, Communities and Local Government, 62% of occupied dwellings in 2023 were condensing-combi boilers.

We can also assume that most of these boilers are fueled by gas for central heating and hot water, as in 2023, natural gas consumption in the UK was 63.5 billion cubic meters.

A standard error code indicates an ignition failure of the boiler. If your boiler can’t ignite the fuel, it can’t produce heat. This failure to ignite could be due to several reasons, such as:

• No gas supply (e.g. gas meter valve closed or outage)
• A faulty ignition electrode or spark generator
• Issues with the gas valve
• Condensate pipe blockage causing flame detection failure (especially in cold weather)

Activating lockout mode means that your boiler stops trying to ignite the fuel, which can be a safety hazard.

Low Water Pressure

Combi boilers need to maintain a constant water pressure level to ensure they operate as efficiently as possible. For combi boilers, the usual water pressure level to maintain is between 1.0 and 1.5 bar when cold.

If it drops too low, your boiler will activate its lockout mode and need to be repressurised.

The potential reasons why your boiler is losing pressure include:

• There may be a leak somewhere in the system
• You’ve recently bled a radiator and lost pressure
• The filling loop wasn’t closed fully after repressurisation

Make sure to address why your boiler’s system is losing pressure before you reset it.

Overheating Or Safety Thermostat Tripped

When your boiler’s system climbs too high, it will activate lockout mode. Reasons why your boiler’s system is overheating include:

• Blocked or seized pump
• Airlocks in the system
• Limescale build-up in the heat exchanger
• Failed temperature sensors (NTC sensors)

Resetting without addressing the root issue may cause repeated lockouts or permanent damage.

Pump Or Flow Issues

Your boiler’s pump needs to circulate its water throughout your home. If an issue is left unaddressed for an extended period, your home’s heating system may overheat or even break down.

Reasons for potential flow issues include:

• The pump is stuck or broken
• There’s an airlock or blockage in the pipes
• Or a flow sensor has failed.

Flue Or Fan Problems

Your boiler uses a fan to expel dangerous combustion gases through the flue.

If it can’t, a sensor detects poor airflow and shuts down the boiler. The reason why your combi boiler has done this includes:

• The fan is faulty or obstructed
• The air pressure switch has failed
• The flue is blocked (common in winter due to ice or debris)

This fault is critical to safety and must be resolved before a reset will be successful.

Sensor Or PCB (Control Board) Faults

Temperature sensors (NTC), flue gas sensors, or the main control board (PCB) may fail, leading to:

• False readings
• Loss of communication between components
• Uncontrolled temperature rise or shutdown

Frozen Condensate Pipe

In cold weather, the external condensate pipe, which carries acidic wastewater from combustion, may freeze.

This backs up fluid into the boiler and triggers a lockout.

There are several signs your condensate pipe is blocked, including:

• Gurgling noises,
• No heating,
• Ignition failure,
• And an error code.

To fix this issue, you can gently thaw the pipe by pouring lukewarm water over the blocked area.

Now that we understand why your boiler might need a reset, here’s how to perform one.

Performing A Reset Of Your Combi Boiler

There are multiple reset procedures for combi boilers. Also, depending on their age and model, they can differ between brands.

While each reset procedure will differ slightly, the general steps are ultimately the same.

Step One: Error Code

Before resetting your combi boiler, take note of the error code. You can do this by snapping a photo or jotting down a note in your boiler’s manual.

Missing this step won’t affect the reset process; it’s just in case the issue reoccurs or you need to contact a Gas Safe registered engineer.

Step Two: Reset The Boiler

As mentioned, there are numerous methods of resetting combi boilers. However, three main methods are relatively standard among the brands, and include:

Reset Button

More common nowadays, combi boilers will have a dedicated reset button located on the front of the unit.

Usually, the process to reset the boiler requires pressing and holding the reset button (marked with a ⟲ symbol or a flame with a line through it) for about 5 seconds, until the error code clears or the display flashes.

Dial Reset

Generally found on older combi boiler models or entry-level units, a dial reset is usually integrated into the main selector.

To reset these combi boilers, you will likely need to turn a selector dial to the reset position for a few seconds, which will clear the error message and return the unit to its usual heating mode.

Manual Reset:

Older models may have a small manual button on the boiler’s panel that must be pressed firmly.

If everything has gone perfectly, reigniting the boiler will take a minute or two.

After the boiler has returned to its usual state, check that the hot water and heating systems are working correctly.

Also, always review your combi boiler’s manual as it will detail the exact process for resetting your unit.

However, if this hasn’t removed the error code and it has reappeared, you can consider performing a manual reset.

Step Three: Turn Off The Power

While this additional step won’t be in the manual, you might need to turn off your boiler at its power source.

Close to your boiler should be a fuse spur. If you’re uncertain what a fuse spur is, it’s a square white box with a large switch in the middle.

Flip this switch on and off. Allow a few seconds for the boiler to shut down.

Sometimes, a boiler is simply plugged into a socket, and you just need to flip the switch.

If you cannot locate your boiler’s plug point, try switching it off and on at the distribution board, also known as:

• Panelboard
• Circuit breaker panel
• Breaker panel
• Electric panel,
• Fuse box,
• Or DB board/box.

Once you’ve turned the power back on, your combi boiler should be reset successfully.

But if you still get the same error message, you will want to do some more troubleshooting.

Further Troubleshooting If Your Boiler Fails To Reset

As with everything in life, the simplest tasks can become more complicated. If you’ve reset your combi boiler and you’re still getting error codes, you will want to perform a few quick checks:

Identify The Error Code

You only want to reset your combi boiler if it is in lockout mode. Make sure to double-check what the error code means.

Usually, the manufacturer will include a comprehensive list of error codes in their manual.

If you’ve lost your manual or are having trouble finding a solution, try some simple checks before calling a professional. Such as:

Check The Gas Supply

A simple check is to see if your home’s main gas supply valve is fully open. Your home’s gas mains should be fully open.

Another way to check for a gas supply issue in your home is to turn on other gas appliances, such as a kitchen stove.

If you suspect a gas supply issue, contact your gas provider. There might be a local supply issue in your area.

However, if you smell gas, turn off the supply immediately and call for help.

Check Water Pressure

Most combi boilers have a pressure gauge on the front panel, either as a dial or analogue gauge, a digital screen, or, on older models, a physical gauge located under the unit.

The combi reading is between 1.0 and 1.5 bar when the system is cold.

If the water pressure reading is below 1.0 bar, your boiler might need to be repressurised.

On the other hand, if your combi boiler’s reading is too high, above 2.5 bar, you will want to bleed a radiator in your home to lower the pressure.

Check The Power Supply

It could be an electrical issue if your boiler doesn’t turn back on after the reset.

Ensure the boiler is plugged into a working power socket and no circuit breakers have tripped.

For those who turned off their boiler via the fuse spur switch, a fuse could have blown if flipping the switch had not restored power to the boiler.

While most of these checks can be completed relatively quickly, if you’re struggling to reset your boiler, we highly recommend calling an expert for help.

Call WarmZilla’s Professionals For A Chat

Rather than struggling to reset your combi boiler, you can call one of our professionals to troubleshoot the problem.

However, if you both discover a more serious issue, the professional on the phone will suggest sending a Gas Safe registered engineer to your home within 48 hours to reset your boiler.