Glow-worm Energy Regular Fault codes & diagnostics

34 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Regular Natural Gas 12-25 kW 2015 onwards Discontinued
GC Numbers 41-019-2141-019-2241-019-2341-019-2441-019-25

Replaced by: Energy7 Regular

Download the Glow-worm Energy Regular manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
3 Emergency 27 High 4 Medium

Which version do you have?

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
41-019-21 ENERGY 12r 2015–present
41-019-22 ENERGY 15r 2015–present
41-019-23 ENERGY 18r 2015–present
41-019-24 ENERGY 25r 2015–present
41-019-25 ENERGY 30r 2015–present

All 34 documented codes

Tap any card for details

Connection

Your boiler's internal computer is unable to talk to the control panel, meaning the unit cannot receive any instructions to turn on.

High Engineer only £180-350

Parts commonly replaced

  • Main PCB
  • User Interface Display Panel
  • Connecting Ribbon Cable

Related codes

F.00

Your boiler has stopped heating because it is struggling to accurately read the temperature of the water flowing through its internal system.

High Engineer only £150-250

Parts commonly replaced

  • NTC Flow Temperature Sensor
  • Wiring harness

Related codes

F.01

Your boiler has stopped working because it is unable to accurately measure the temperature of the water returning to it from your radiators.

High Engineer only £120-220

Parts commonly replaced

  • Return NTC thermistor
  • Wiring harness

Related codes

F.10

Your boiler has stopped working because it is unable to accurately measure the temperature of the water flowing through the system due to a connection fault.

High Engineer only £120-220

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness

Related codes

F.11

Your boiler has detected a faulty connection in the pipework sensor that measures how hot your water is, which is preventing it from heating your home correctly.

High Engineer only £120-220

Parts commonly replaced

  • Return temperature sensor
  • Wiring harness

Related codes

F.13

Your boiler is struggling to detect the temperature of your hot water storage tank, so it has paused the water heating feature to prevent it from overheating.

Medium Engineer only £120-200

Parts commonly replaced

  • DHW cylinder NTC sensor
  • Wiring harness

Related codes

F.20

Your boiler has detected that it is running too hot and has automatically shut itself down to prevent any damage.

High Engineer only £150-300

Parts commonly replaced

  • NTC Temperature Sensor
  • Central Heating Pump
  • Primary Heat Exchanger

Related codes

F.23

Your boiler has detected that the water flowing out is significantly hotter than the water returning, suggesting the internal pump is struggling to move water around your heating system properly.

High Engineer only £150-300

Parts commonly replaced

  • Central heating pump
  • NTC thermistors
  • System filter

Related codes

F.24

Your boiler is shutting itself down because the water inside is heating up much faster than it can circulate away, which could lead to overheating.

High Engineer only £150-350

Parts commonly replaced

  • Central heating pump
  • System filter
  • NTC thermistor
  • Heat exchanger

Related codes

F.25

Your boiler has detected that the internal exhaust temperature is too high and has shut itself down to prevent overheating.

High Engineer only £150-300

Parts commonly replaced

  • Flue gas temperature sensor
  • Heat exchanger
  • Main PCB

Related codes

Showing 11–20 of 34
F.27

Your boiler has detected an issue with its internal flame sensor and has safely shut itself down to prevent gas from being wasted or building up.

High Engineer only £150-300

Parts commonly replaced

  • Flame rectification electrode
  • Ignition lead
  • Main printed circuit board (PCB)

Related codes

F.28

Your boiler is failing to ignite the flame that produces heat because it cannot detect gas or a spark during the startup process.

High Engineer only £150-350

Parts commonly replaced

  • Ignition lead
  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

F.29

Your boiler is attempting to light but is failing to stay on, which means your heating and hot water have stopped working.

High Engineer only £120-250

Parts commonly replaced

  • Ignition lead
  • Spark electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

F.32

Your boiler has detected that the internal fan responsible for venting exhaust gases is not spinning at the correct speed or is jammed.

High Engineer only £150-300

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Main PCB

Related codes

F.49

Your boiler's communication wires are experiencing a electrical short or power clash, meaning the boiler and your thermostat can no longer 'talk' to each other.

High Engineer only £120-250

Parts commonly replaced

  • eBUS wiring
  • Main PCB
  • External thermostat/controller

Related codes

F.61

Your boiler has detected an electrical fault in the part that controls the gas supply, meaning it has safely shut itself down to prevent ignition.

Emergency Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Wiring harness
  • Main printed circuit board (PCB)

Related codes

F.62

Your boiler has detected an issue where it cannot safely stop the gas flow when it needs to shut down, which means it has locked itself out to keep your home safe.

Emergency Engineer only £200-450

Parts commonly replaced

  • Gas valve
  • Main electronics PCB

Related codes

F.63

Your boiler's main control computer is experiencing a critical internal data error and can no longer safely operate the heating system.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

F.64

Your boiler has detected an internal electrical reading error, which means it has stopped working to prevent potential damage to its main control systems.

High Engineer only £180-350

Parts commonly replaced

  • NTC Temperature Sensor
  • Main Printed Circuit Board (PCB)

Related codes

F.65

Your boiler has detected that its internal computer is getting too hot and has stopped working to prevent further damage.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Showing 21–30 of 34
F.67

Your boiler has detected an internal electronic error and cannot reliably confirm if the burner flame is lit, so it has shut itself down as a safety precaution.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Wiring harness

Related codes

F.68

Your boiler is struggling to keep a steady flame, which is causing it to stop firing because it cannot safely maintain the burning process.

High Engineer only £120-250

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve

Related codes

F.70

The boiler's internal computer has lost its identification settings, usually because a new control board was fitted without being programmed correctly for your specific unit.

High Engineer only £100-200

Parts commonly replaced

  • PCB
  • Coding resistor

Related codes

F.71

Your boiler is confused because it is getting incorrect temperature readings, so it has shut down to prevent overheating.

High Engineer only £120-220

Parts commonly replaced

  • Flow temperature sensor
  • Return temperature sensor

Related codes

F.72

Your boiler is struggling to accurately measure its internal temperature, causing it to shut down to prevent potential overheating.

High Engineer only £150-250

Parts commonly replaced

  • Flow temperature sensor
  • Return temperature sensor
  • Wiring harness

Related codes

F.77

Your boiler has detected an issue with the system that removes waste gases, meaning it cannot operate safely and has shut itself down to prevent a fire or carbon monoxide hazard.

Emergency Engineer only £150-350

Parts commonly replaced

  • Flue non-return valve
  • Condensate trap assembly

Related codes

F.78

Your boiler is struggling to communicate with your hot water controller, which is preventing it from heating your water correctly.

Medium Engineer only £120-220

Parts commonly replaced

  • Hot water NTC sensor
  • Wiring harness
  • Link box

Related codes

F.83

Your boiler has detected that it is not heating up correctly when it fires, which usually means there is air trapped inside or the water level is too low.

High Engineer only £120-250

Parts commonly replaced

  • NTC temperature sensor
  • System pump
  • Flow sensor

Related codes

F.84

Your boiler is confused because the temperature sensors are detecting heat in the wrong places, likely due to a wiring mix-up or a faulty sensor connection.

High Engineer only £120-220

Parts commonly replaced

  • NTC thermistor sensor
  • Wiring harness

Related codes

F.85

Your boiler has detected that its temperature sensors are either disconnected or have been attached to the wrong pipes, meaning it cannot accurately judge how hot the water is.

High Engineer only £120-220

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring harness

Related codes

Showing 31–34 of 34
F.86

Your boiler has detected that the connection to your underfloor heating system is interrupted or the sensor responsible for checking its status is faulty.

Medium Engineer only £120-250

Parts commonly replaced

  • Underfloor heating sensor
  • Wiring harness
  • Main PCB

Related codes

F.87

Your boiler is failing to detect the internal spark needed to ignite the flame, meaning it cannot start up to provide heat or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition lead
  • Ignition electrode
  • Wiring harness

Related codes

F.88

Your boiler has lost the connection to the internal valve that controls its gas supply, meaning it cannot safely start up to heat your home.

High Engineer only £150-250

Parts commonly replaced

  • Gas valve
  • Wiring harness

Related codes

F.91

Your boiler has lost the ability to read the temperature of your hot water cylinder because of a faulty connection or wiring issue.

Medium Engineer only £120-200

Parts commonly replaced

  • Cylinder temperature sensor
  • NTC thermistor wiring harness

Related codes

44 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

d.02 Diagnostic Your boiler is taking a short, programmed break to prevent it from switching on and off too frequently, which is a normal part of its operation. d.94 Diagnostic Your boiler has performed a routine reset of its internal memory to clear previous error history, which is a normal administrative function. P.01 Diagnostic Your boiler is simply running through its normal ignition sequence to begin heating your home. P.02 Diagnostic Your boiler is currently in the process of safely igniting its burner to begin heating your home. P.03 Diagnostic Your boiler is currently operating in a temporary testing mode at its maximum power setting, rather than a standard fault state. P.04 Diagnostic Your boiler is currently running at its maximum power setting to help the system reach its target temperature, and this is simply an information status rather than a fault. P.05 Diagnostic Your boiler is currently refilling its internal water system, which is a normal process that happens automatically. P.06 Diagnostic Your boiler is currently performing a brief automatic process to clear trapped air from the system pipes. P.07 Diagnostic Your boiler is currently running a routine automated process to clear trapped air from the system, and no action is required on your part. P.10 Diagnostic Your boiler has detected an issue with its internal safety monitoring system and has automatically shut down to prevent any potential risk. S.0 Status Your boiler is perfectly healthy and is simply waiting for a signal from your thermostat to turn on the heating or hot water. S.01 Status Your boiler is currently performing a standard pre-heating safety check and will likely start up normally in a few moments. S.02 Status Your boiler is simply preparing to heat your home by circulating water through the pipes before it fires up. S.03 Status Your boiler is currently in the process of attempting to light the flame to heat your home. S.04 Status Your boiler is operating correctly and is currently firing up to heat your radiators. S.05 Status Your boiler is currently performing a normal cooling-down process to safely clear excess heat after your heating has turned off. S.06 Status Your boiler is currently cooling down its internal components after finishing a heating cycle, which is a normal part of its shutdown process. S.07 Status Your boiler is currently performing a standard process where it circulates water after the heating has switched off to ensure residual heat is safely distributed. S.08 Status Your boiler is currently taking a short, scheduled break to manage its internal temperature before restarting the heating process. S.20 Status Your boiler is currently operating normally as it processes a request to heat your hot water. S.21 Status Your boiler is currently just warming up its ventilation system before firing up to provide heat or hot water. S.22 Status Your boiler is currently preparing to heat your water by running the internal pump, which is a normal part of the startup sequence. S.23 Status Your boiler is currently in the process of lighting the flame to heat your water, which is a normal part of its routine operation. S.24 Status Your boiler is currently operating normally to heat your hot water supply. S.25 Status Your boiler is currently running its internal safety cooling cycle after heating water, which is a normal part of the shutdown process. S.26 Status Your boiler is currently cooling itself down after providing hot water, which is a normal part of the shutdown process. S.27 Status Your boiler is currently cooling itself down by running the internal pump after having just finished heating your water. S.28 Status Your boiler has temporarily paused the burner while it adjusts the water temperature, which is a normal part of its internal operation. S.30 Status Your boiler is perfectly healthy, but it is currently waiting for a signal from your wall-mounted thermostat to tell it to turn the heating on. S.31 Status Your boiler is currently in standby mode because your thermostat is not requesting any heating or hot water at the moment. S.32 Status Your boiler is temporarily pausing because the internal fan that clears exhaust gases is not spinning at the exact speed required to operate safely. S.34 Status Your boiler has detected that the temperature is low enough that it has automatically switched on to prevent internal pipes from freezing. S.39 Status Your boiler is signalling that the external control for your underfloor heating system is not communicating correctly, which may prevent that specific heating zone from turning on. S.42 Status Your boiler has detected that the flap which controls exhaust fumes is stuck shut, meaning it cannot safely release gases outside. S.46 Status Your boiler has automatically activated its built-in winter protection mode because the internal temperature has dropped, and it is currently running at a low level to prevent the pipes from freezing. S.53 Status Your boiler has temporarily stopped working because it cannot move water around your heating system efficiently, often due to low pressure or blocked circulation. S.54 Status Your boiler has detected that the water is not circulating properly through your heating system, likely because the pressure is too low or a valve is closed. S.88 Status Your boiler is currently running an automated air-removal cycle to ensure the system is operating efficiently. S.91 Status Your boiler has been accidentally set to a showroom demonstration mode, which prevents it from firing up to provide heating or hot water. S.96 Status Your boiler is currently running a self-check program and has temporarily paused heating to ensure it is operating safely and correctly. S.98 Status Your boiler is currently performing an internal health check and has paused your heating system to ensure everything is operating safely. S.99 Status Your boiler is currently running an internal system check to ensure all its components are communicating correctly. S.108 Status Your boiler is currently running its internal safety ventilation cycle and should restart normally on its own. S.109 Status Your boiler is currently in a power-saving standby mode and is working exactly as it should.