65 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
The fault code is already on your display
Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →
The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.
| GC number | Appliance (register name) | Produced |
|---|---|---|
| 41-406-58 | Greenstar 27i System Compact ErP | 2015–present |
| 41-406-59 | Greenstar 27i System Compact ErP LPG | 2015–present |
Appliance names and production years are taken from the UK Product Characteristics Database (the SAP/SEDBUK register). Where a GC number is also printed in this model's own manufacturer manual, both sources were checked to agree.
Tap any card for details
Your boiler has detected an internal computer error and needs a professional inspection by the manufacturer.
Your boiler has detected that it is getting too hot too often and has locked itself down as a safety precaution to prevent damage.
Your boiler's main control unit has encountered a communication error and is unable to operate safely.
Your boiler is operating correctly and is currently heating the water for your radiators.
Your boiler is currently operating normally as it heats up your hot water for taps and showers.
Your boiler is temporarily pausing its heating to prevent turning on and off too quickly, which is usually a normal safety feature rather than a fault.
Your boiler is currently in a temporary holding state and is waiting for a signal from your heating controls, such as your thermostat or programmer, to tell it to start.
Your boiler is temporarily pausing because the water inside it has already reached the temperature you requested.
Your boiler is struggling to clear exhaust gases before ignition, so it has paused itself to ensure it is safe to operate.
Your boiler has temporarily stopped working because the water pressure inside the heating system has dropped too low.
Your boiler is currently locked in a testing mode used by engineers to check the flue system, which prevents it from heating your home normally.
Your boiler has temporarily stopped working because it has detected a blockage or a safety issue with the airflow and exhaust gases.
Your boiler has detected a safety issue with the removal of exhaust gases and has automatically shut down to prevent the buildup of dangerous fumes.
Your boiler has detected that the water inside is heating up far too quickly, so it has safely shut itself down to prevent damage.
Your boiler has detected that the water leaving the boiler is much hotter than the water returning, usually caused by a restriction in water flow or trapped air.
Your boiler has detected a blockage or issue preventing air from flowing properly through the system, so it has safely shut down to prevent damage.
Your boiler has successfully lit the flame, but the water inside is not heating up as expected.
Your boiler has temporarily stopped working because it detected a timing error during its safety checks, which usually requires a qualified engineer to investigate.
Your boiler has detected an internal computer glitch and needs a professional heating engineer to safely reset or replace the faulty control part.
Your boiler has detected an internal computer error and needs a professional engineer to diagnose and resolve the issue.
Your boiler has detected that the air supply needed for safe combustion has been interrupted while it was running, causing it to shut down for safety.
Your boiler has temporarily stopped operating because it has detected an issue with the rate at which heat is moving through the system.
Your boiler is struggling to detect water movement, which suggests it cannot properly circulate heat to your radiators or taps.
Your boiler's computer system has detected an internal processing error and has shut down to prevent any unsafe operation.
Your boiler has accidentally entered a special technician-only mode used for testing parts, which stops it from heating your home normally.
Your boiler is struggling to light because it is detecting an issue with the ignition process, causing it to lock itself out for safety.
Your boiler is currently resetting or performing its initial startup sequence, which typically happens when power is first restored after a shutdown.
Your boiler has detected that the water temperature is changing too drastically between two different points, causing it to shut down to prevent potential damage.
Your boiler has detected an internal electronic error that is preventing it from starting up correctly.
Your boiler has detected that the internal fan was running when it should have been switched off, suggesting a potential communication issue with the control board.
Your boiler has detected that it is still sensing a flame even when it should be turned off, which can indicate a small internal electrical or sensor issue.
Your boiler has automatically shut down because the water inside it has become dangerously hot.
Your boiler has temporarily shut down because an internal safety sensor detected that the water temperature got too hot, usually caused by a blockage in water flow.
Your boiler has temporarily stopped working because it cannot properly read one of its internal temperature sensors.
Your boiler has temporarily locked itself out to protect itself because it was asked to restart too quickly after shutting down.
Your boiler has temporarily locked out because it has started up repeatedly without successfully staying on, which is usually a safety precaution to prevent damage.
Your boiler has detected that the incoming cold water is warmer than the hot water it is producing, which usually points to a sensor or valve issue.
Your boiler has detected an issue with the sensor that monitors exhaust gases, so it has safely shut down to prevent incorrect operation.
Your boiler is struggling to accurately measure the temperature of the water being heated for your taps and shower.
Your boiler's internal computer has lost contact with the main control panel, preventing it from starting up correctly.
Your boiler's computer has detected a serious internal fault that prevents it from operating safely, requiring a qualified professional to inspect or replace the electronic control system.
Your boiler has detected that the internal fan is spinning too slowly to safely clear waste gases, so it has shut down as a precaution.
Your boiler's internal fan is spinning faster than it should, which has caused the system to shut down for safety.
Your boiler has stopped working because the internal component responsible for pushing air through the system is failing to start.
Your boiler has lost connection to the weather sensor outside, but it should still continue to keep your home warm using its backup settings.
Your boiler is temporarily locked out because it cannot detect water movement or pressure change when the internal pump starts up.
Your boiler has lost communication with the device that tells it how much water is inside, so it has shut down to prevent damage.
Your boiler has temporarily stopped working because it has detected an incorrect temperature reading from one of its internal sensors.
Your boiler has lost its connection to an essential safety internal plug, meaning it currently cannot communicate correctly with its control system.
Your boiler has detected that your radiators are not transferring heat properly, causing the water returning to the unit to be much cooler than the water leaving it.
Your boiler has temporarily stopped working because it has detected an electrical fault with the sensor that measures the temperature of the water flowing through the system.
Your boiler has detected that hot water is flowing in the wrong direction or circulating incorrectly, meaning it cannot heat your home properly.
Your boiler is having trouble 'reading' the temperature of the incoming water, which is causing it to stop operating correctly to prevent a potential error.
Your boiler has detected that the water inside the system is getting much hotter than it should be, so it has shut itself down to prevent damage.
Your boiler has temporarily shut down because an internal safety monitor detected that the internal water temperature got too hot.
Your boiler has tried to light several times but has been unable to detect a flame, causing the system to shut down for safety.
Your boiler has detected that the exhaust gases are getting too hot, too quickly, so it has turned itself off to prevent internal damage.
Your boiler has detected that hot gases are building up inside the system while the water meant to be heating your home is staying cold, so it has safely shut down to prevent overheating.
Your boiler has temporarily stopped because the hot water inside the system has become much hotter than it should be.
Your boiler has detected that the water inside isn't warming up as expected after it fires up, so it has stopped trying to prevent potential damage.
Your boiler's internal computer has encountered a software or electronic error and can no longer control the heating properly.
Your boiler has detected a safety signal inside before it has even attempted to light, so it has safely locked itself out to prevent starting.
Your boiler is still detecting a flame even though it has tried to turn the gas supply off, which is a safety concern that requires an engineer.
Your boiler has detected that a safety valve controlling the gas supply is not sealing properly, so it has safely shut itself down to prevent a gas buildup.
Your boiler is showing this code simply because the reset button was held down for too long or pressed by mistake, which has confused the internal software.
Monthly cover means no unexpected bills when your boiler breaks down.
Affiliate links. We may earn a commission at no extra cost to you.
BoilerFaultCodes