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Glow-worm Boiler Issues: Errors and Fault Codes

Glow-worm boilers tend to be reliable but, like with all appliances, problems can occur and they can develop a fault at any time. Should a fault develop with your Glow-worm boiler, a fault code might appear to help you identify the problem and to enable you to inform your engineer what went wrong. Boiler fault codes also help your engineer to cut down on investigation time, which means they should be able to get to the bottom of the issue quickly so that your home isn’t left without heating or hot water for too long. 

If you’re currently experiencing a problem with your Glow-worm boiler and a fault code has appeared, the tables below should help you find out what the error code means. 

Glow-Worm Energy Boiler Range Fault Codes

FAULT CODEDESCRIPTION / POSSIBLE CAUSE
F.00Fault with flow temperature sensor. NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness or NTC sensor defective.
F.01Fault with return temperature sensor. NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness or NTC sensor defective.
F.10Short circuit flow temperature sensor. NTC defective, short circuit in the cable harness, cable or casing. 
F.11Short circuit return temperature sensor. NTC defective, short circuit in the cable harness, cable or casing.
F.12 or F.91Short circuit cylinder temperature sensor. NTC defective, short circuit in the cable harness, cable or casing.
F.13Short circuit domestic hot water cylinder temperature sensor. NTC defective, short circuit in the cable harness, cable or casing.
F.20Safety switch off. Overheating temperature reached. Incorrect earth connection between cable harness and product, flow or return NTC defective (loose connection), black discharge via ignition cable, ignition plug or ignition electrode. 
F.22Safety switch off. Low water pressure in the boiler. Insufficient or no water in the boiler, water pressure sensor defective or cable to the pump or to the water pressure sensor is loose, not connected or defective. 
F.23Safety switch off. Temperature difference too great NTC1/NTC2. Pump blocked, insufficient pump output, air in boiler or flow and return NTC sensor connected the wrong way round. 
F.24Safety switch off. Temperature rise too fast. Pump blocked, insufficient pump output, air in boiler, system pressure too low or non-return valve blocked or incorrectly installed. 
F.25Safety switch off. Flue gas temperature too high. Break in plug connection for optional flue gas safety temperature limiter (STB) or break in cable harness. 
F.27Safety switch off. Fault in flame detection. Moisture in the electronics, electronics flame monitor defective or gas solenoid valve is leaking.
F.28Ignition unsuccessful when starting up. Gas meter defective or gas pressure monitor has triggered, air in gas, gas flow pressure too low, thermal isolator device (TAE) has triggered, incorrect gas restrictor, incorrect spare gas valve, fault on gas valve, multiple plug on PCB incorrectly plugged in, break in cable harness, ignition system defective, isolation current interrupted, incorrect earthing or electronics defective.
F.29Flame loss. Gas supply temporarily stopped, flue gas recirculation, incorrect earthing of product or ignition transformer has spark failure. 
F.32Fan frost protection function active. Fan speed outside tolerance values. Plug or fan not plugged in correctly, multiple plug on PCB not plugged in correctly, break in cable harness, fan blocked, hall sensor defective or electronics defective. 
F.33Fan frost protection function active. Air pressure switch fault. Pressure monitor has not switched or has switched at fan speed value that’s too high (insufficient air supply). Pressure monitor not plugged in correctly, pressure monitor defective, hose removed from between the pressure monitor and silencer or air/flue pipe blocked. 
FA9eBUS fault. Voltage too low. Short circuit on eBUS, eBUS overload or two power supplies with different polarities on the eBUS.
F.61Gas valve control system fault. Short circuit to earth in cable harness for the gas valve, gas valve defective (colls shorted to earth) or electronics defective.
F.82Gas valve switch-off control fault. Delayed switch-off of gas valve, delayed extinguishing of flame signal, gas valve leaking or electronics defective.
F.83EEPROM fault. Electronics defective.
F.64Fault with electronics, sensor or analogue to digital convertor. Flow or return NTC short circuited or electronics defective.
F.85Electronics temperature too high. Electronics overheating due to external influences or electronics defective.
F.67Valve sent back by ASIC is incorrect. Implausible flame signal or electronics defective.
F.88Unstable flame (analogue input). Air in gas, gas flow pressure too low, incorrect air ratio, incorrect gas restrictor or ionisation flow interruption. 
F.70Invalid product code (DSN). Display and PCB replaced at same time and Device Specific Number not reset or wrong or missing output range coding resistance. 
F.71Fault with flow/return temperature sensor. Flow temperature sensor signalling constant value, flow temperature sensor incorrectly positioned on supply pip or flow temperature sensor defective. 
F.72Deviation in the water pressure sensor/return temperature sensor. Flow/return temperature difference too great. Flow and/or return temperature sensor defective.
F.73Water pressure sensor not connected or has short circuited. Interruption or short circuit of water pressure sensor or interruption or short circuit to GND in supply line to water pressure sensor or water pressure sensor defective. 
F.74Electrical problem in the water pressure sensor. Line to water pressure sensor has a short circuit to 5V/24V or internal fault in the water pressure sensor. 
F.75Pressure sensor fault. Pressure switch defective.
F.78Safety cut-out in primary heat exchanger is defective. Safety cut-out feedback does not match the gas valve feedback.
F.77Condensate or smoke. No response, flue non-return flap defective. 
F.78Interruption to DHW outlet sensor at external controller. UK ink box is connected but hot water NTC not bridged. 
F.83Fault with burner temperature sensor. When burner starts, the temperature change registered at the flow or return temperature sensor is non-existent or too small. Insufficient water in product or the flow or return temperature is in the wrong position on the pipe.
F.84Fault with flow/return temperature sensor. Valves not consistent. Flow and return temperature sensors signalling implausible values. Flow and return temperature sensors have been inverted or have not been correctly installed. 
F.85Fault with temperature sensor. The flow and/or return temperature sensors have been installed on the same pipe – temperature sensor not connected or is connected incorrectly.
F.86Underfloor heating contact is open or sensor is defective or disconnected.
F.87Electrodes not connected or are connected incorrectly or short circuit in the cable harness. 
F.88Gas valve fault. Gas valve not connected or is connected incorrectly or short circuit in the cable harness. 
F.89Pump fault. Pump not connected or is connected incorrectly, incorrect pump connected or short circuit in the cable harness.

Glow-worm Betacom Boiler Range Fault Codes 

FAULT CODEDESCRIPTION / POSSIBLE CAUSE
Red LED onLockout – low water pressure. Make sure pressure is above 1.5 bar and reset boiler. 
Red LED flashingDHW (domestic hot water) temperature control knob in service position. Turn the DHW control knob into temperature range. OR overheat – check both overheat stats.
Yellow LED flashingTurn DHW (domestic hot water) control know into temperature range and turn CH temperature control knob into power (reset position) and wait 30 seconds before turning into either summer or temperature position. 
Yellow LED onFlame present on the burner.
Green LED onBoiler ready for operation.
Green LED offNo power to boiler. Check for 230 volts into the appliance and check fuse on PCB.
Green LED flashingBoiler in stand-by – reset position.

Glow-worm Betacom A Boiler Range Fault Codes

FAULT CODEDESCRIPTION / POSSIBLE CAUSE
F00Flow heating temperature sensor fault.
F01Return heating temperature sensor fault.
F10Flow heating temperature sensor fault.
F11Return heating temperature sensor fault.
F20Overheating fault.
F22Low water pressure.
F23Water circulation fault.
F24Water circulation fault.
F26Fault in gas valve.
F27Flame detection fault.
F28Ignition fault.
F29Loss of flame during operation.
F32Incorrect air pressure.
F49eBUS voltage fault.
F61Fault in the main board.
F62Fault in the main board.
F63Fault in the main board.
F64Fault in the main board.
F65Fault in the main board.
F67Fault in the main board.
F68Fluctuation of flame signal.
F70User interface incompatible with the main board.
F71Flow heating temperature sensor fault.
F72Permanent temperature difference between flow and return heating sensors. 
F73Heating circuit pressure sensor fault.
F74Heating circuit pressure sensor fault.
F76Thermal fuse fault.
F77Fault in gas valve motor. 
F83No water in the installation.
F84Permanent temperature difference between flow and return heating sensors. 
F85Flow and return heating sensor fault.
F86Underfloor heating contact fault.
ErrUser interface fault. 

Glow-worm Betacom C Boiler Range Fault Codes

FAULT CODEDESCRIPTION / POSSIBLE CAUSE
Temperature 30 flashingFault on CH thermistor.
Temperature 40 flashingFault on DHW thermistor.
Temperature 50 flashingFault on outside sensor.
Temperature 60 flashingLow system pressure.
Temperature 70 flashingFault on APS.
Temperature 80 flashingOverheat open circuit.
Temperature 90 flashingFlame or gas failure.

Glow-worm Flexicom cx, hx and sx Boiler Range Fault Codes

FAULT CODEDESCRIPTION / POSSIBLE CAUSE
F1Ignition fault.
F3Fan unable to reach ignition speed.
F4Ignition fault.
F5Overheat fault.
F6Central heating flow thermistor fault. 
F7Domestic hot water thermistor fault.
F9Water pressure sensor fault – blocked flow filter or pump fault.
F10Central return flow thermistor fault.
F11Flow or return thermistor fault.
F13PCB memory or sensing fault.
F14Gas valve defective.
F15eBUS voltage failure. 
F22Low water pressure or ignition temperature rise too slow.
F24Central heating return temperature 90 degrees.
F25Circulation fault.
F43Generic error.
F70Software incompatible.
F73Unable to see pump active.
F77Condensate pump error.

Glow-worm Ultracom2  sxi, cxi and 35 Store Boiler Range Fault Codes

FAULT CODEDESCRIPTION / POSSIBLE CAUSE
F00Flow heating temperature sensor fault.
F01Return heating temperature sensor fault.
F10Flow heating temperature sensor fault.
F11Return heating temperature sensor fault.
F20Overheating fault.
F22Low water pressure.
F23Water circulation fault.
F24Water circulation fault.
F26Fault in gas valve.
F27Flame detection fault.
F28Ignition fault.
F29Loss of flame during operation.
F32Incorrect air pressure.
F49eBUS voltage fault.
F61Fault in the main board.
F62Fault in the main board.
F63Fault in the main board.
F64Fault in the main board.
F65Fault in the main board.
F67Fault in the main board.
F68Fluctuation of flame signal.
F70User interface incompatible with the main board.
F71Flow heating temperature sensor fault.
F72Permanent temperature difference between flow and return heating sensors. 
F73Heating circuit pressure sensor fault.
F74Heating circuit pressure sensor fault.
F76Thermal fuse fault.
F77Fault in gas valve motor. 
F83No water in the installation.
F84Permanent temperature difference between flow and return heating sensors. 
F85Flow and return heating sensor fault.
F86Underfloor heating contact fault.
ErrUser interface fault. 

Glow-worm Ultracom sxi, cxi and hxi Boiler Range Fault Codes

FAULT CODEDESCRIPTION / POSSIBLE CAUSE
F1Ignition fault.
F3Fan unable to reach ignition speed.
F4Ignition fault.
F5Overheat fault.
F6Central heating flow thermistor fault.
F9Water pressure sensor fault – blocked flow filter or pump fault.
F10Central return flow thermistor fault.
F11Main board connection fault.
F13PCB memory or sensing fault.
F14Gas valve control defective.
F15eBUS voltage failure.
F22Low water pressure or ignition temperature rise too slow.
F25Circulation fault.
F43Generic error.
F70Software incompatible.
F73Unable to see pump active.
F77Condensate pipe error.
No display or ErLoose connection x51.

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