Keston Boiler Error Codes: Causes & Fixes

The most common Keston boiler error codes UK homeowners and landlords see are E01 for ignition failure, E37, E67 or E44 for low water pressure, E03 for overheat, E05 or E28 for fan issues, and E07 for flue overheat. 

These codes help you identify the issue so you can restore heating and hot water safely and quickly.

Some can be fixed with a quick pressure top-up or reset, while others need a Gas Safe registered engineer. Understanding the code puts you in a stronger position and helps stop minor faults turning into larger repair bills. 

Many people find that having a boiler cover plan ready means they can get professional help without the worry of unexpected costs when a more serious fault shows up.

Keston Boiler Error Codes: A Quick Overview

Here is a clear table of the Keston boiler error codes you are most likely to encounter, with a short plain-English description of what each one usually means.

Codes can vary slightly by model, so always check your handbook if the display looks different. The table above covers the codes that appear most often across UK homes.

Keston Boiler Error Codes: Causes & How to Fix

Below you will find dedicated sections for the main Keston boiler error codes. Each one explains what the code means, the usual causes, and clear numbered steps you can take. Safety comes first: if you smell gas, turn the supply off at the meter if it is safe and call the National Gas Emergency Service on 0800 111 999. 

For any gas-related work or if a code returns after a reset, contact a Gas Safe registered engineer.

E01 Ignition Failure

The E01 error code means the boiler has attempted to light five times and has not succeeded. Heating and hot water will stop until the fault is cleared.

Common causes include a problem with the gas supply, a dirty or faulty ignition electrode, low gas pressure, a blocked burner, or a frozen condensate pipe in cold weather.

1. Check that other gas appliances in the home are working. If none are, contact your gas supplier.
2. Look outside for the condensate pipe and check whether it is frozen. Pour warm (not boiling) water along it to thaw any ice.
3. Press and hold the reset button on the boiler for a few seconds.
4. Listen for the fan and the spark attempting to light.
5. If the code returns after one or two resets, switch the boiler off and call a Gas Safe engineer. Do not keep resetting.

A frozen condensate pipe is a frequent winter cause and is often the quickest thing to check.

E37, E67, E44 Or F1 Low Water Pressure

These error codes mean the water pressure in the sealed heating system has dropped below the safe level. The boiler will not operate until the pressure is restored.

Causes include a small leak from a radiator, valve or pipe joint, natural pressure loss after bleeding radiators, or a problem with the expansion vessel.

1. Look at the pressure gauge on the boiler. It should sit between 1.0 and 1.5 bar when the system is cold.
2. Locate the filling loop (usually a flexible hose with two valves under or near the boiler).
3. Open both valves slowly until the gauge reaches about 1.2–1.5 bar.
4. Close both valves tightly.
5. Reset the boiler if needed and check that heating and hot water return.
6. Monitor the pressure over the next day or two. If it drops again there is likely a leak that needs professional attention.

Topping up is a straightforward job most homeowners can manage, but repeated drops should not be ignored.

E03 Boiler Overheat

The E03 fault code means the boiler has detected that the water inside has got too hot and has locked out for safety.

Common reasons are closed valves on the heating circuit, air in the system, incorrect water pressure, a stuck or failing pump, or restricted flow.

1. Turn the boiler off and allow it to cool completely (this can take 30–60 minutes).
2. Check system pressure and top up if needed.
3. Make sure all radiator valves are fully open.
4. Bleed any radiators that feel cold at the top.
5. Reset the boiler once it is cool.
6. If E03 returns, do not keep using the boiler. Call a Gas Safe engineer to check the pump, flow and heat exchanger.

E05 Or E28 Fan Failure

The E05 or E28 code indicates the boiler cannot detect fan rotation. The fan is vital for safe combustion and removing flue gases.

Causes include a seized or failing fan motor, loose connectors, or debris in the fan.

Do not attempt to repair the fan yourself. Switch the boiler off and arrange for a Gas Safe engineer to diagnose and replace the fan if required. Running without a working fan is unsafe.

E07 Flue Overheat

The E07 error code means the flue temperature has risen higher than it should (usually more than 10°C above the return temperature).

Causes include poor combustion, a heat exchanger problem, restricted flue, or a faulty flue sensor.

1. Check the external flue terminal for any visible blockage and clear it if safe to do so.
2. Reset the boiler once.
3. If the code returns, an engineer needs to inspect the flue, heat exchanger and combustion.

E02 False Flame

The E02 fault code means the boiler is detecting a flame signal when none should be present.

Causes can include a problem with the power supply, a sticky gas valve, or a faulty electrode giving false readings.

Reset once if the boiler allows it. If the code returns, a Gas Safe engineer will need to check the gas valve, electrodes and control box.

E18 Flow Overheat

The E18 code (common on C40 and C55 models) means the flow temperature has risen too high.

Causes are usually poor water circulation, airlocks, or a failing pump.

1. Check and top up pressure.
2. Ensure all valves are open and bleed radiators.
3. Reset once.
4. If it returns, an engineer needs to check circulation and the pump.

E24 Pressure Lost Multiple Times

The E24 error code means the water pressure has dropped four times within 24 hours.

This almost always points to a leak somewhere in the system or boiler. Top up the pressure once, but if it drops again call an engineer to find and repair the leak.

E26 Flame Dropout

The E26 fault code means the flame has gone out during operation.

Causes include flue or air terminal obstruction, a blocked or frozen condensate drain, or low gas supply (especially on LPG).

1. Check and clear any obvious flue blockages if safe.
2. Thaw the condensate pipe if needed.
3. Reset once.
4. If the code returns, call a Gas Safe engineer.

E08 Flame Circuit Error

The E08 code points to a problem in the flame monitoring circuit, often linked to the control box.

This requires a Gas Safe engineer to diagnose and repair.

E09 Valve Drive Error

The E09 error code means there is a problem with the gas valve or its drive from the control box.

Only a Gas Safe registered engineer should investigate this.

Having a boiler cover plan in place can make a real difference when codes like these appear. Instead of facing unexpected call-out and repair costs, you simply report the fault and a qualified engineer is arranged. For many UK homeowners and landlords this peace of mind, plus the included annual service, helps prevent small pressure or sensor issues from becoming expensive breakdowns.

How To Reset A Keston Boiler Safely

Most Keston models have a clearly marked reset button on the control panel. Press and hold it for a few seconds until the display clears or the boiler restarts. Only reset once or twice for the same code. If the fault returns, switch the boiler off and seek professional help. Continuous resetting can put extra strain on components and may hide a more serious problem.

Which Keston Boiler Faults Should Be Left to a Professional?

While low-pressure codes such as E37, E67, E44 and F1 can sometimes be resolved by carefully topping up the heating system, several Keston error codes indicate faults that should not be investigated as a DIY repair.

It is time to contact a Gas Safe registered engineer if you experience:

• Repeated E01 or E26 faults, as ongoing ignition or flame dropout problems may involve the gas supply, ignition components, burner or flue system.
• E03 or E18 overheat codes that return, particularly after checking the system pressure, opening radiator valves and allowing the boiler to cool.
• E05 or E28 fan faults, as the fan is essential for supplying air and safely removing combustion gases.
• E07 flue overheat, which may require the flue, combustion process, heat exchanger or associated components to be professionally checked.
• E02, E08 or E09, as false flame detection, flame circuit faults and gas valve errors involve safety-critical boiler components.
• E24 or recurring low-pressure faults, as repeated pressure loss can indicate a leak or another underlying problem within the heating system.

A single reset may occasionally clear a temporary fault, but a Keston boiler that repeatedly locks out is telling you that the underlying issue has not been resolved. A qualified engineer can identify the cause of the fault and carry out the necessary repairs before the problem leads to further boiler damage or another breakdown.

How to Prevent Keston Boiler Error Codes

• Keep track of pressure changes rather than only checking when the boiler locks out: A gradual fall in system pressure can lead to faults such as E37, E67, E44 or F1. Checking the gauge periodically can help you identify an issue before the boiler shuts down.
• Investigate repeated pressure loss promptly: If the system needs frequent topping up or the pressure drops several times over a short period, arrange for the cause to be investigated. Persistent pressure loss can eventually trigger faults such as E24.
• Maintain unrestricted water flow around the heating system: Avoid leaving radiator valves or isolation valves closed after maintenance or decorating. Restricted circulation can contribute to overheating faults such as E03 and E18.
• Look out for changes in radiator performance: Radiators that suddenly develop cold spots, become noisy or heat inconsistently may indicate trapped air or restricted circulation. Dealing with these problems early can help reduce strain on the boiler and its pump.
• Prepare the condensate pipe for cold weather: A frozen or blocked condensate drain can contribute to ignition and flame dropout faults. Checking the external pipework before periods of freezing weather can help reduce the likelihood of this type of problem.
• Pay attention to unreliable boiler ignition: If the boiler begins taking several attempts to fire, occasionally fails to ignite or cuts out shortly after starting, have the issue checked before it develops into a recurring E01 or E26 fault.
• Keep the external flue terminal area clear: Periodically check that there are no obvious obstructions, such as vegetation or debris, around the terminal. Never attempt to dismantle or alter the flue yourself.
• Do not ignore unusual fan behaviour: New humming, rattling or mechanical noises when the boiler starts may indicate that the fan is beginning to wear. Having this investigated early may help prevent E05 or E28 fan faults.
• Arrange an annual boiler service: An annual service carried out by a Gas Safe registered engineer can help identify developing issues with the Keston boiler’s ignition system, pump, sensors, fan, combustion and other key components before they result in an unexpected fault code.
• Avoid using repeated resets as a long-term solution: If the same Keston error code continues to return, record the code and arrange for the underlying fault to be diagnosed. Continually resetting the boiler may temporarily clear the display without addressing the cause of the problem.

Be Prepared When Your Keston Boiler Shows a Fault Code

A Keston boiler error code can sometimes point to a straightforward issue, such as low system pressure or a frozen condensate pipe. However, codes linked to ignition failure, overheating, fan faults, flue problems or gas valve issues may require a qualified engineer and can lead to unexpected repair costs.

That is where having the right protection in place can make a difference. A PlusHeat boiler cover plan can help you avoid being caught off guard when your boiler develops a fault that cannot be resolved with a simple reset or pressure top-up.

Rather than waiting until an E01, E05, E28 or another Keston fault leaves you without heating or hot water, take a look at our boiler cover plans and choose the level of cover that suits your home or rental property. Having cover in place before a breakdown occurs can provide greater peace of mind when professional help is needed.

Frequently Asked Questions

What should I do if my Keston boiler shows a code that is not listed in the manual?

Note the exact code and any lights or symbols, then check the official Keston support resources or contact a Gas Safe engineer. Different ranges (C36, C40, C55, S30) can use slightly different displays, so matching the full code to your exact model is important.

Can a power cut cause Keston boiler error codes?

Yes. After a power interruption some boilers display a general lockout, control box error or E04 code. Once power is stable, a single reset often clears it. If the code returns, the control board or wiring may need checking.

How often should I check my Keston boiler pressure to avoid error codes?

A quick look at the pressure gauge once a month is sensible, especially before winter. Aim for 1.0–1.5 bar when the system is cold. Catching a slow pressure drop early helps prevent E37, E44 or F1 from appearing.

Do Keston error codes differ between combi and system boilers?

Many core codes (pressure, ignition, fan, overheat) are shared, but system models may show additional codes related to the outside sensor or boiler chip card. Always refer to the specific handbook for your model.

Is it safe to keep using the boiler if an error code clears after a reset?

Only if the code does not return and the boiler runs normally with stable pressure and even heating. Any recurring code, unusual noises, or smell of gas means stop using it and call a qualified engineer.