Glow-worm SUSTAIN 30c Fault codes & diagnostics

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

Combi Gas 2015-present
GC Number 47-019-33
Download the Glow-worm SUSTAIN 30c manualThe official installation and service manual (PDF), the document these fault codes were read from. PDF

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38 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
47-019-33 SUSTAIN 30c 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.

All 42 documented codes

Tap any card for details

Connection

Your boiler's electronic control board is currently failing to 'talk' to the display screen, meaning it cannot receive commands or provide status updates.

High Engineer only £150-300

Parts commonly replaced

  • User Interface PCB
  • Main Control PCB
  • Wiring harness

Related codes

F.00

Your boiler is unable to measure the temperature of the water inside it, so it has safely shut down to prevent overheating.

High Engineer only £120-180

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring harness

Related codes

F.01

Your boiler is struggling to accurately measure the temperature of the water returning to it, so it has stopped working to prevent potential overheating.

High Engineer only £150-250

Parts commonly replaced

  • Return temperature sensor
  • 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 faulty electrical connection or sensor.

High Engineer only £120-220

Parts commonly replaced

  • Flow temperature sensor (NTC thermistor)
  • Wiring harness

Related codes

F.11

Your boiler has stopped working because it is unable to accurately read the temperature of the water returning to it, causing it to shut down for safety.

High Engineer only £120-220

Parts commonly replaced

  • Return temperature sensor
  • Wiring harness

Related codes

F.12

Your boiler is struggling to detect the temperature of your hot water cylinder because of a faulty connection or wiring issue.

Medium Engineer only £120-220

Parts commonly replaced

  • NTC Cylinder Sensor
  • Wiring harness

Related codes

F.13

Your boiler has lost the ability to detect the temperature of your hot water tank, so it has turned off the hot water service to prevent overheating.

Medium Engineer only £120-220

Parts commonly replaced

  • NTC temperature sensor
  • Wiring loom
F.20

Your boiler has automatically shut down because it detected that the internal temperature has become too high, preventing it from overheating.

High DIY-safe £100-280

What to check first

  1. Check that your radiator valves are fully open to allow water to flow.
  2. Ensure there is no air trapped in the system by bleeding your radiators.
  3. Press the reset button (indicated by a flame with a cross through it) to restart the boiler.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • NTC Temperature Sensor

Related codes

F.22

Your boiler has temporarily stopped working because the water pressure inside the system has dropped too low.

High DIY-safe

What to check first

  1. Locate the filling loop valves underneath your boiler.
  2. Open both valves gently to let water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close both valves tightly and reset the boiler.

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor
  • Expansion vessel

Related codes

F.23

Your boiler has shut down because it detected that the water temperature is changing too quickly or unevenly, often due to a circulation problem.

High Engineer only £120-350

Parts commonly replaced

  • Circulation Pump
  • NTC Thermistor Sensors
  • Heat Exchanger (Cleaning)

Related codes

Showing 11–20 of 42
F.24

Your boiler has switched itself off because the water inside it is heating up too quickly, which usually means the water isn't flowing through the system properly.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar on the gauge
  3. Try resetting the boiler to see if the fault clears

Parts commonly replaced

  • Circulation pump
  • Flow/Return thermistor
  • Main heat exchanger (cleaning)

Related codes

F.25

Your boiler has shut down because the internal exhaust gases are getting too hot, which is a safety feature to prevent damage to the appliance.

High Engineer only £120-350

Parts commonly replaced

  • Heat exchanger
  • Flue gas NTC sensor
  • Burner seals

Related codes

F.27

Your boiler has sensed a flame when there shouldn't be one, or the device that monitors the fire is faulty, causing the system to shut down for safety.

High Engineer only £100-280

Parts commonly replaced

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

Related codes

F.28

Your boiler is failing to light the fuel inside, meaning it cannot produce heat or hot water because it hasn't detected a flame.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed circuit board (PCB)

Related codes

F.29

Your boiler is trying to start but the flame keeps going out, meaning it cannot produce heat or hot water.

High Engineer only £150-300

Parts commonly replaced

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

Related codes

F.32

Your boiler has detected that the internal fan responsible for clearing exhaust gases is not spinning at the correct speed to operate safely.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)

Related codes

F.33

Your boiler has sensed it is too cold and the fan is stuck trying to protect the internal pipes from freezing.

High Engineer only £120-250

Parts commonly replaced

  • Air pressure switch
  • Fan assembly
  • Venturi tube

Related codes

F.49

Your boiler's internal communication system is struggling to transmit data because the electrical signal between its components is too weak.

High Engineer only £120-250

Parts commonly replaced

  • eBUS connection cable
  • Main PCB
  • External controller

Related codes

F.61

Your boiler has detected a communication issue with the part that controls the flow of gas, and it has stopped working for your safety.

High Engineer only £150-300

Parts commonly replaced

  • Gas valve
  • Wiring harness
  • Main PCB

Related codes

F.62

Your boiler has detected an issue with the valve that controls the gas supply, causing it to shut down for safety reasons.

High Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Showing 21–30 of 42
F.63

Your boiler's internal computer is experiencing a memory error, meaning it has lost its settings and cannot safely manage the heating process.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB

Related codes

F.64

Your boiler has detected an internal computer processing error, causing it to shut down for safety reasons to prevent incorrect operation.

High Engineer only £200-450

Parts commonly replaced

  • Main printed circuit board (PCB)
  • Wiring harness
  • Sensor wiring

Related codes

F.65

Your boiler has detected that its internal computer components are overheating, so it has safely shut itself down to prevent any damage.

High Engineer only £150-300

Parts commonly replaced

  • Main printed circuit board (PCB)
  • Wiring harness
  • Internal fan

Related codes

F.67

Your boiler has detected an internal electronic error while trying to monitor the flame, causing it to shut down for safety.

High Engineer only £200-450

Parts commonly replaced

  • Main printed circuit board (PCB)

Related codes

F.68

Your boiler is struggling to keep the flame alight consistently, causing it to shut down for safety reasons.

High Engineer only £150-300

Parts commonly replaced

  • Flame rectification electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

F.70

Your boiler's computer has lost its identity settings, preventing it from knowing how to function correctly.

High Engineer only £120-250

Parts commonly replaced

  • User Interface PCB
  • Main PCB

Related codes

F.71

Your boiler has stopped working because it is unable to accurately measure the temperature of the water flowing through your heating system.

High Engineer only £150-250

Parts commonly replaced

  • Flow/Return NTC Sensor
  • Wiring harness

Related codes

F.72

Your boiler is struggling to accurately measure its internal water pressure or temperature, preventing it from operating safely.

High Engineer only £180-350

Parts commonly replaced

  • Water pressure sensor
  • NTC return temperature sensor
  • Printed Circuit Board (PCB)

Related codes

F.73

Your boiler is unable to read the water pressure level because the sensor responsible for checking it is faulty or disconnected, preventing the boiler from starting safely.

High Engineer only £150-250

Parts commonly replaced

  • Pressure sensor
  • Wiring harness

Related codes

F.74

Your boiler is having trouble accurately reading the internal water pressure due to a faulty electrical connection or sensor.

High Engineer only £150-250

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness lead

Related codes

Showing 31–40 of 42
F.75

Your boiler is struggling to detect the water pressure inside the system because the sensor is failing to provide a clear reading.

High Engineer only £150-250

Parts commonly replaced

  • Pressure sensor
  • Expansion vessel

Related codes

F.76

Your boiler has detected a failure in a vital safety component that prevents the system from overheating, causing it to shut down to keep your home safe.

High Engineer only £180-350

Parts commonly replaced

  • Overheat thermostat
  • Heat exchanger sensor
  • Wiring harness

Related codes

F.77

Your boiler has detected that water is failing to drain away properly or there is an issue with the exhaust system, causing it to shut down for safety.

High Engineer only £120-250

Parts commonly replaced

  • Condensate trap
  • Condensate pump
  • Flue sensor

Related codes

F.78

Your boiler has lost the connection to the sensor that monitors your hot water temperature.

Medium Engineer only £120-220

Parts commonly replaced

  • DHW NTC sensor
  • Wiring harness
  • PCB

Related codes

F.83

Your boiler has detected that the water temperature readings are inconsistent or not changing as expected when the burner is lit, so it has shut down to prevent damage.

High Engineer only £150-250

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring harness

Related codes

F.84

Your boiler is struggling to accurately measure the temperature of the water circulating through your heating system, so it has stopped working as a safety precaution.

High Engineer only £150-250

Parts commonly replaced

  • NTC thermistor (flow/return sensor)
  • Wiring harness

Related codes

F.85

Your boiler has detected that a temperature sensor is not providing the correct data, which is preventing the system from safely heating your water.

High Engineer only £120-200

Parts commonly replaced

  • NTC temperature sensor
  • Wiring harness

Related codes

F.86

Your boiler has detected an issue with the separate switch or connection that tells it to provide heat to your underfloor heating system.

Medium Engineer only £120-250

Parts commonly replaced

  • External underfloor heating switch
  • Wiring harness
  • Main PCB

Related codes

F.87

Your boiler is failing to ignite correctly because the probe responsible for lighting the gas is not working as it should, meaning your heating and hot water will not turn on.

High Engineer only £120-220

Parts commonly replaced

  • Ignition electrode
  • Ignition lead
  • PCB

Related codes

F.88

Your boiler is unable to control the gas supply it needs to ignite, which means your heating and hot water have stopped working.

High Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Main PCB
  • Wiring harness

Related codes

Showing 41–42 of 42
F.89

Your boiler has detected that the water pump responsible for circulating heat is not working correctly, which means your heating and hot water will stop functioning until the issue is addressed.

High Engineer only £250-450

Parts commonly replaced

  • Central heating pump
  • Wiring harness
  • Printed Circuit Board

Related codes

F.91

Your boiler is struggling to detect the temperature of your hot water cylinder because there is an electrical connection issue with the sensor.

High Engineer only £120-220

Parts commonly replaced

  • Cylinder temperature sensor
  • Wiring loom

Related codes

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