Glow-worm EnergySaver Combi Fault codes & diagnostics

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

Combi Natural Gas Discontinued

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26 High
Just want the most common Glow-worm EnergySaver Combi faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 26 documented codes

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0 8

Your boiler has stopped working because the pipe that drains away excess liquid is blocked, likely due to debris or frozen water if it is cold outside.

High DIY-safe £0-120

What to check first

  1. Check the white plastic pipe leading outside to see if the end is submerged in water or blocked by debris.
  2. If it is freezing weather, gently pour warm (not boiling) water over the external pipe to melt any ice blockages.
  3. Ensure any external collection tanks or 'soakaways' are not overflowing or backed up.

Parts commonly replaced

  • Condensate trap
  • External pipe insulation
  • Flexible condensate hose
Full explanation for 0 8
1 2

Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.

High DIY-safe £0-£120

What to check first

  1. Locate the filling loop (a flexible silver hose) underneath or near the boiler.
  2. Slowly open the valves on the filling loop until you hear water flowing.
  3. Watch the pressure gauge and close the valves once it reaches 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve
Full explanation for 1 2
02

Your boiler has failed to ignite, meaning it cannot produce heat for your radiators or hot water.

High DIY-safe £120-280

What to check first

  1. Check if other gas appliances, like a cooker, are working to ensure gas is reaching the property.
  2. Ensure your pre-payment gas meter has sufficient credit.
  3. Press the 'Reset' button (often marked with a flame symbol) on the boiler control panel.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Probe
Full explanation for 02
03

Your boiler's internal computer has encountered an electronic error and can no longer control the heating and hot water Safely.

High Engineer only £250-450

Parts commonly replaced

  • Automatic Control Module (PCB)
  • Wiring Harness

Related codes

Full explanation for 03
04

Your boiler has lost its electrical power supply or experienced a sudden interruption, causing it to shut down safety.

High DIY-safe £0-120

What to check first

  1. Check if there has been a local power cut in your street or home
  2. Check your property's main fuse box (consumer unit) to see if a circuit breaker has tripped
  3. Ensure the boiler’s fused spur switch (usually near the boiler) is turned on
  4. Try resetting the boiler by turning the selector knob to the 'Reset' position for 5 seconds

Parts commonly replaced

  • Internal Glass Fuse
  • Printed Circuit Board (PCB)
  • External Fused Spur
Full explanation for 04
05

Your boiler's computer brain has encountered a serious internal error and cannot safely operate the system.

High Engineer only £280-450

Parts commonly replaced

  • Automatic Control Module (PCB)
  • Wiring Harness

Related codes

Full explanation for 05
06

Your boiler's internal computer has encountered a critical error and can no longer control the heating and hot water functions safely.

High Engineer only £250-£450

Parts commonly replaced

  • Automatic Control Module (PCB)
  • Wiring harness

Related codes

Full explanation for 06
07

Your boiler's main internal computer has developed a serious technical error and can no longer control the heating process safely.

High Engineer only £250-£450

Parts commonly replaced

  • Automatic Control Module (ACM)
  • Main Printed Circuit Board (PCB)
Full explanation for 07
13

Your boiler's main internal computer has developed a malfunction and is no longer able to control the heating process safely.

High Engineer only £250-£450

Parts commonly replaced

  • Automatic Control Module (PCB)
  • Wiring Harness
Full explanation for 13
14

Your boiler’s main computer brain has developed an internal electrical error and has stopped the unit from working for safety.

High Engineer only £250-£450

Parts commonly replaced

  • Automatic Control Module (PCB)
  • Wiring Harness

Related codes

Full explanation for 14
Showing 11–20 of 26
15

Your boiler's main internal computer has encountered a critical error and is unable to operate the system safely.

High Engineer only £250-£450

Parts commonly replaced

  • PCB (Printed Circuit Board)
  • Automatic Control Module
Full explanation for 15
16

Your boiler's main internal computer has developed a software or hardware failure and can no longer control the heating and hot water.

High Engineer only £280-450

Parts commonly replaced

  • Automatic Control Module (PCB)
  • Wiring Harness

Related codes

Full explanation for 16
17

Your boiler's main control computer has developed an internal electrical fault and can no longer safely operate the system.

High Engineer only £280-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Automatic Control Module

Related codes

Full explanation for 17
18

Your boiler has sensed that the water inside is getting much too hot and has shut down as a safety precaution.

High Engineer only £90-250

Parts commonly replaced

  • Flow Thermistor (NTC Sensor)
  • Circulation Pump
  • Main Heat Exchanger
Full explanation for 18
19

Your boiler has shut down because the water returning from your radiators is getting too hot, indicating a potential blockage or pump issue.

High Engineer only £120-250

Parts commonly replaced

  • Return thermistor (NTC sensor)
  • Circulation pump
  • Heat exchanger
Full explanation for 19
24

Your boiler has detected that the water is heating up too quickly or not circulating properly through the system, causing a large temperature gap between the pipes.

High DIY-safe £120-450

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 pressure gauge
  3. Bleed all radiators to remove trapped air that could be blocking water flow

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger
  • Flow/Return Thermistors
Full explanation for 24
25

Your boiler is heating up much faster than it should and has shut down to prevent itself from overheating.

High DIY-safe £120-350

What to check first

  1. Check if your radiator valves are open
  2. Ensure your boiler pressure is between 1.0 and 1.5 bar
  3. Gently bleed your radiators to remove any trapped air

Parts commonly replaced

  • Circulation Pump
  • Flow Thermistor (NTC Sensor)
  • Main Heat Exchanger
Full explanation for 25
26

Your boiler's electronic brain has developed a software or hardware error and can no longer control the heating and hot water safely.

High Engineer only £250-£450

Parts commonly replaced

  • Automatic Control Module (PCB)
  • Wiring Harness
Full explanation for 26
28

Your boiler has stopped working because the internal fan, which safely exhausts fumes, is not spinning correctly or communicating with the system.

High Engineer only £200-£450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for 28
29

Your boiler has stopped working because the internal fan that moves waste gases out of the flue is not spinning.

High Engineer only £280-450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for 29
Showing 21–26 of 26
30

Your boiler detects a flame when it shouldn't, which is causing it to shut down for safety.

High Engineer only £120-300

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Printed Circuit Board (PCB)
Full explanation for 30
31

Your boiler has detected a fault with a temperature sensor and has shut down as a safety precaution, meaning you currently have no heating or hot water.

High Engineer only £100-£190

Parts commonly replaced

  • Flow Thermistor (NTC Sensor)
  • Connecting Wiring Loom

Related codes

Full explanation for 31
32

Your boiler has detected a fault with the sensor that monitors water temperature returning from your radiators, preventing the system from heating up properly.

High Engineer only £90-160

Parts commonly replaced

  • Heating Return Thermistor (NTC sensor)
  • Wiring Harness
Full explanation for 32
36

Your boiler has stopped working because a sensor that measures the temperature of the water heading to your radiators is sending an incorrect or broken signal.

High Engineer only £110-190

Parts commonly replaced

  • Heating Flow Thermistor (NTC sensor)
  • Connecting wiring harness
Full explanation for 36
37

Your boiler has detected that a sensor monitoring the temperature of the water returning to the unit is giving an incorrect reading or has failed, causing the system to stop working as a safety precaution.

High Engineer only £95-170

Parts commonly replaced

  • Return thermistor (NTC sensor)
  • Wiring harness / sensor connections
  • Main PCB (if signal processing has failed)
Full explanation for 37
41

Your boiler's internal computer has developed a fault and can no longer communicate with the rest of the system safely.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Automatic Control Module
Full explanation for 41