51 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 |
|---|---|---|
| 47-019-55 | ULTIMATE 3 30c-A (H-GB) | 2017–present |
| 47-019-57 | ULTIMATE 3 35c-A (H-GB) | 2017–present |
Tap any card for details
Your boiler has lost the ability to accurately measure the temperature of the water flowing through it, so it has shut down to ensure safety.
Your boiler has stopped working because a sensor that measures the temperature of the water coming back into the system has sent an incorrect reading.
Your boiler has stopped working because it is unable to accurately measure the temperature of the water flowing through the system due to a faulty sensor connection.
Your boiler has detected an electrical fault with one of its temperature sensors, which is preventing it from safely monitoring water circulation.
Your boiler is struggling to detect the temperature of your hot water because of a faulty electrical connection or sensor reading.
Your boiler has detected that it is getting too hot and has automatically switched itself off to prevent any damage or danger.
Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.
Your boiler has detected that the water is heating up too unevenly, so it has safely shut itself down to prevent any damage to its internal components.
Your boiler has detected that the water inside is heating up far too quickly and has shut itself down as a safety measure to prevent damage.
Your boiler has detected that the exhaust gases leaving the system are dangerously hot and has shut itself down to prevent overheating.
Your boiler is failing to detect a flame when it tries to light, so it has safely shut itself down to prevent gas from building up.
Your boiler is trying to start but cannot get the flame to stay lit, so it has shut itself down for safety.
Your boiler is failing to stay lit, which means it cannot produce hot water or heating because the flame is cutting out during operation.
Your boiler has detected that the internal fan is spinning at an incorrect speed, possibly due to freezing conditions or a mechanical issue, and has paused operation to prevent damage.
Your boiler's communication system is experiencing an electrical signal failure, meaning the control panel or external thermostat cannot send instructions to the boiler safely.
Your boiler has detected a problem with the internal part that controls the flow of gas, so it has safely shut itself down to prevent ignition.
Your boiler has detected an issue with the internal safety mechanism that controls the gas flow, so it has safely shut itself down to prevent operation.
Your boiler's main control computer is having trouble reading or writing its internal memory, which prevents it from operating safely.
Your boiler has detected an internal communication error between its internal computer and its sensors, meaning it cannot process information correctly to run safely.
Your boiler's control system has detected that its internal electronic components are overheating, so it has shut down to protect itself from damage.
Your boiler has detected an internal electronic error while trying to monitor the flame, causing it to shut down for safety.
Your boiler has detected that the flame inside is flickering or unstable, causing it to shut down for safety reasons.
Your boiler's computer has lost track of what specific model it is, preventing it from functioning correctly.
Your boiler is struggling to read its own water temperature, so it has shut down to prevent overheating or damage.
Your boiler is having trouble accurately measuring the water pressure or temperature, which prevents it from operating safely.
Your boiler's internal water pressure sensor is failing to communicate, which means the system cannot accurately monitor its water levels and will stop working until resolved.
Your boiler is having trouble 'reading' the water pressure inside the system because the sensor that measures it has developed an electrical fault.
Your boiler is struggling to detect the water pressure inside the system because the sensor is not giving a clear reading.
Your boiler has detected an issue with the drainage of water produced during operation or a blockage in the internal system that clears away exhaust fumes.
Your boiler is having trouble communicating with the external controls responsible for regulating your hot water temperature.
Your boiler has detected that there is not enough water circulating inside it to safely ignite the flame.
Your boiler is receiving conflicting temperature readings from its sensors, so it has stopped working to prevent potential damage.
Your boiler has detected that one of its internal heat sensors is reporting a conflicting or illogical reading, causing it to shut down to prevent potential overheating.
Your boiler has detected an issue with the separate underfloor heating system connected to it, preventing that part of your heating from working correctly.
Your boiler is failing to light the burner because it cannot detect the spark needed to start the heating process.
Your boiler has detected a problem with the internal mechanism that controls the gas flow, meaning it cannot safely ignite to provide heating or hot water.
Your boiler is unable to move water through the system because the pump is not functioning correctly, which will stop your heating and hot water from working.
Your boiler's internal computer is failing its own startup check, meaning the system cannot safely operate the heating or hot water.
Your boiler has likely experienced an internal electrical fault or a component failure that has caused a safety fuse on the main control board to blow.
Your boiler has stopped because the water pressure inside the system has dropped too low to operate safely.
Your boiler is failing to ignite the main gas burner, which means you will have no heating or hot water until it is repaired.
Your boiler has lost electrical power, which is usually caused by an issue with the mains supply or a blown internal fuse.
Your boiler is not receiving electrical power or has an internal blown fuse, meaning it cannot start the ignition process.
Your boiler has become too hot and has automatically shut down for safety purposes.
Your boiler has switched itself off because it has reached an unsafe temperature or it has detected a faulty component in its safety system.
Your boiler has stopped working because it cannot safely clear away waste gases, preventing it from firing up.
Your boiler is unable to safely clear exhaust fumes, which prevents it from firing up to provide heat or hot water.
Your boiler is failing to light the gas flame or cannot detect that the flame has started, so it has shut down for safety.
Your boiler is failing to light the gas or cannot confirm that a flame is present, meaning the system has shut down for safety.
Your boiler is failing to start up because the small ignition flame is not lighting correctly.
Your boiler's small starter flame is failing to stay lit, which prevents the main burner from turning on to provide heating and hot water.
Not faults — these are normal operating states. Tap to expand.
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