87 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 |
|---|---|---|
| 41-116-05 | Microsystem 15 RFFI | 2000–2007 |
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 that it is running too hot and has automatically shut down to prevent damage to its internal parts.
Your boiler has detected that the water inside the system is becoming too hot and has automatically shut itself down to prevent damage.
Your boiler has detected that it is running too hot and has automatically shut down to prevent damage to its internal parts.
Your boiler is struggling to move water around your heating system because the flow is blocked, restricted, or the pump is failing.
Your boiler is struggling to push water around your heating system because the flow is blocked or restricted.
Your boiler is struggling to move water around your heating system effectively, usually because there is trapped air, a blockage, or low water pressure.
Your boiler has detected that the water pressure inside the system is dangerously high, which can cause internal leaks or safety valve discharge.
Your boiler has lost the ability to measure the temperature of the water circulating through your radiators, so it has turned itself off as a precaution.
Your boiler has lost the ability to measure the temperature of the water returning to it from your radiators, so it has shut down to stay safe.
Your boiler is having trouble communicating with the outdoor weather sensor, which helps it adjust your heating based on the temperature outside.
Your boiler has detected that the external temperature safety switch, often connected to underfloor heating, has cut the connection to the system.
Your boiler is struggling to accurately monitor the temperature of the water circulating through your radiators, so it has stopped working as a safety precaution.
Your boiler has detected that water is not moving around your heating system fast enough, often due to trapped air or a closed valve.
Your boiler has detected that hot water is not flowing around your heating system properly, so it has shut down to prevent overheating.
Your boiler has detected that water is not flowing through the heating system correctly, which is preventing it from safely warming your home.
Your boiler is struggling to move water around your heating system effectively, which is causing it to stop for protection.
Your boiler is having trouble reading the temperature of the water used for your taps and shower because a sensor connection is interrupted.
Your boiler's computer has encountered a memory error, meaning it has lost its internal settings and cannot safely operate your heating or hot water.
Your boiler's internal computer is struggling to talk to its main control board, which has caused the system to stop working entirely.
Your boiler's internal computer is experiencing a communication error and has shut down to prevent potential damage to the system.
Your boiler has detected that the reset button has been pressed too many times in a short period, which has triggered a built-in safety lockout to prevent potential damage to the electronic control board.
Your boiler's central computer is experiencing a communication or internal processing fault, causing the system to shut down for safety.
Your boiler's electronic command center is experiencing a communication error and is unable to operate correctly.
Your boiler's central control computer is experiencing a communication fault, preventing it from operating safely.
Your boiler is struggling to communicate with your thermostat because of a loose connection or damaged wiring in the sensor circuit.
Your boiler is having trouble communicating with the temperature sensor for your secondary heating zone, meaning it doesn't know how warm that specific part of your home is.
Your boiler is struggling to read the temperature from an external wall controller or zone sensor, which prevents it from knowing when to turn the heating on.
Your boiler has stopped working because it cannot light the internal flame needed to heat your water.
Your boiler has detected a flame signal when it is not supposed to be running, which indicates a potential safety issue with the internal electronics or gas controls.
Your boiler is detecting that the flame is not burning correctly on the burner, which prevents it from heating your water safely.
Your boiler is struggling to light because it cannot detect a flame, which means you currently have no heating or hot water.
Your boiler has tried and failed to light the flame twice, so it has locked itself out for safety.
Your boiler has stopped because the flame inside has gone out unexpectedly while running.
Your boiler has detected that the water inside the unit is getting too hot, so it has safely shut itself down to prevent damage.
Your boiler is struggling to push air through its internal system effectively, preventing it from safely lighting the flame.
Your boiler is struggling to read the temperature for a secondary heating zone, meaning that specific part of your home may not heat up correctly.
Your boiler is having trouble communicating with the temperature sensor for your secondary heating zone, which may prevent that part of your home from heating up properly.
Your boiler is having trouble communicating with one of its internal temperature sensors, which may cause your heating or hot water to work inconsistently.
Your boiler is having trouble 'sensing' the temperature of the water returning from your radiators, which prevents it from heating your home correctly.
Your boiler is having trouble communicating with the temperature sensor for your secondary heating area, which may cause that part of the home to struggle to heat up correctly.
Your boiler is having trouble reading the water temperature for one of the specific heating zones in your home, which may cause that part of the system to stop working correctly.
Your boiler has detected that the water temperature in your secondary heating circuit is higher than it should be, causing the system to shut down to prevent damage.
Your boiler has detected that the water temperature in one part of your heating system is higher than it should be, causing it to shut down for safety.
Your boiler has disabled your heating system because it cannot detect or communicate with the controls that request heat for your radiators.
Your boiler has detected that the water pressure in your heating system is too low to operate safely, so it has shut down to protect itself.
Your boiler has detected a communication error with its internal combustion control system, meaning it cannot safely regulate the burner.
Your boiler has stopped working because it is not receiving a supply of gas.
Your boiler is failing to detect water flowing through the system, which means it cannot safely turn on the heating or hot water.
Your boiler is failing to ignite because it cannot properly control the fuel supply needed to create a flame.
Your boiler is failing to light the flame, which means you currently have no heating or hot water until the ignition system is fixed.
Your boiler is struggling to direct heat to your radiators or hot water taps because a valve inside the unit has failed to move into the correct position.
Your boiler is failing to move the water around the system correctly, which means your heating and hot water will not work until the issue is cleared.
Your boiler is failing to detect a flame, which means it cannot safely light or stay running to provide heating and hot water.
Your boiler has detected an issue with its internal electrical grounding connection, which means it has safely shut down to prevent an electrical hazard.
Your boiler is struggling to detect the flame needed to heat your water and has safely shut itself down to prevent a gas buildup.
Your boiler has detected an issue with the ignition process and is currently failing to light the burner to provide heat or hot water.
Your boiler has detected an internal electrical supply fault and will stop working to protect itself.
Your boiler has detected that the internal water filter is blocked, which is preventing water from circulating properly to provide you with heating or hot water.
Your boiler is struggling to clear exhaust gases before firing up, likely due to a blockage or a faulty component that detects airflow.
Your boiler has failed to fire up because it could not successfully light its internal flame after several attempts.
Your boiler is struggling because it cannot detect enough water or water flow within your heating system to operate safely.
Your boiler has detected that the water inside the heating system has become dangerously hot and has shut itself down to prevent damage.
Your boiler has tried to light the flame several times but has been unable to stay running, so it has safely shut itself down to prevent a gas build-up.
Your boiler has detected that the air-intake component is not working, which means the unit cannot safely vent gases or ignite.
Your boiler's computer is having trouble interpreting its own internal signals, which has caused it to shut down for safety reasons.
Your boiler has detected that it is running too hot and has automatically shut down to prevent any internal damage.
Your boiler is struggling to communicate with your wall thermostat, meaning it doesn't know when to turn your heating on or off.
Your boiler is having difficulty controlling the flow of gas needed to ignite or maintain the flame correctly.
Your boiler is struggling to read the temperature of the water inside the system, which currently prevents it from providing your heating or hot water safely.
Your boiler is struggling to detect that there is enough water flowing through its internal system to safely turn on your heating.
Your boiler is struggling to switch between heating your radiators and providing hot water, which means you will likely have no hot water or central heating until it is fixed.
Your boiler is having trouble communicating with its internal timer, which means your scheduled heating programs may not turn on or off as expected.
Your boiler has detected a safety concern and has automatically turned itself off to prevent any risk to your home.
Your boiler has switched off because a safety sensor in your underfloor heating system has detected the water is getting too hot and has triggered an automatic shutdown to prevent damage.
Your boiler is having trouble sensing the correct airflow needed to burn fuel safely, so it has stopped working to prevent a potential hazard.
Your boiler has detected that its internal computer is struggling to confirm that the main control system is operating correctly.
Your boiler has lost the ability to monitor the temperature of your hot water, so it has safely stopped heating it to prevent overheating.
Your boiler has detected a faulty sensor, meaning it cannot correctly measure the temperature of the hot water going to your taps.
Your boiler has lost the connection to a sensor responsible for monitoring the temperature of the water returning from your radiators, and as a result, it has stopped working to protect itself.
Your boiler has detected a flame signal even though it is trying to turn the gas off, which indicates a potential safety issue with the main control system.
Your boiler's main control computer is experiencing a general communication error, causing the system to stop working as a safety precaution.
Your boiler has stopped working because it couldn't light the flame needed to provide heating or hot water.
Your boiler has detected that the water pressure inside the system is too low to run safely and needs to be topped up.
Your boiler has stopped working because the water pressure inside your heating system has dropped too low to operate safely.
Your boiler is struggling because it cannot detect enough water pressure inside the system to safely circulate heat.
Your boiler has detected that it is running much too hot and has automatically switched itself off to prevent internal damage.
Your boiler has detected an internal electronic error before trying to ignite and has safely turned itself off to prevent any risk.
Not faults — these are normal operating states. Tap to expand.
BoilerFaultCodes