Glow Worm Error Codes

glow worm boiler with f.28 error

This article deals with all the Glow Worm error codes you can face from your boiler. The following glow worm error codes contain models, such as Betacom, Ultracom, Flexicom, Xtramax, Compact, Ci, and Xtrafast.

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Glow Worm Boiler Error Codes


Flow temperature sensor

F.10 and F.11

The flow temperature sensor has short-circuited

F.12 and F.91

The cylinder temperature sensor has short-circuited


The domestic hot water cylinder temperature sensor has short-circuited


Safety switch-off process due to overheating


Safety switch-off process due to boiler low water pressure


The safety switch-off process due to temperature difference is too large


Safety switch-off process due to temperature rising too fast


Safety switch-off process due to flue gas temperature being too high


Safety switch-off process due to fault in the flame


Unsuccessful ignition when starting up


Loss of flame


The fan frost protection function is active, meaning that fan speed is outside its tolerance levels


eBus fault because the voltage is too low


There is a fault with the gas valve control system


Fault with the electronics, sensor, or analogue to digital converter


The value sent by ASIC is incorrect


Invalid product code or DSN


Fault with flow or return temperature sensor


Change in the return temperature sensor or water pressure sensor


The water pressure sensor has short-circuited or is not connected


Fault with the pressure sensor


The safety cut out located in the


There is a fault with the fast valve switch


EEPROM fault due to defective electronics

It could also be a fault to the burner temperature sensor


Return or temperature sensor fault


Temperature sensor fault


Electrodes fault


Unstable flame in analogue input, gas valve fault or underfloor heating contact fault


Pump fault

If your boiler ever puts up the following glow worm error codes, then you should know that there is a problem with your condensate pipe

  • F1
  • F4
  • F28
  • F29

Glow Worm Fault Codes & DIY Fixes If Possible

Here is a list of the exact faults from Glow Worm boilers – Most faults will require a Gas Safe registered heating engineer so that is the reason why there isn’t a suggestion for what you should do in these scenarios.

Fault CodesBoiler ModelIssueDIY Fix 
F25Xtramax HE RangeMaximum temperature rise slope  
F26Xtramax HE RangeMaximum delta temperature  
F00Xtrafast 96/120 Range   
F00Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeNo fault  
F02Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeAir flow fault  
F05Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeOverheating  
F06Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeCentral heating thermistor or wiring fault  
F08Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeStorage vessel thermistor or wiring fault  
F09Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeSystem pressure sensor fault  
F10Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeFan fault  
F13Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeMain PCB fault  
F14Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeThe central heating flow temperature is higher than 97 degrees.  
F15Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeGas mechanism fault  
F20Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeCommunication fault 
F13Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxi / Xtramax HEPCB memory fault 
F14Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxi / Xtramax HEGas valve control is defective 
F15Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxi / Xtramax HEE-bus voltage failure 
F25 23All BoilersCirculation fault 
F43Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxiGeneric error 
F70Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxiSoftware incompatibility 
F73Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxiUnable to see pump activate 
F77Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxiCondensate pump error 
F02 / F12Ultracom₂ 35 StoreHot water temperature sensor fault 
F03 / F13 / F79Ultracom₂ 35 StoreStorage tank temperature sensor fault 
F81Ultracom₂ 35 StoreOverheating of the hot water circuit 
No display or ErAll Ultracomloose connection X51 
F24Xtramax HE RangeCentral heating return temperature is higher than 90 degrees 
F25 F26 F11cxi / hxi / sxi / Xtrafast 96/120 / Xtrafast 96/120E1Poor circulation 
F3Ci rangeAir fault 
F2 F3cxi / sxi / hxi range/ Xtramax HEFan fault 
F3cxi / sxi range / Flexicom cx / hx / sx / hxi / Ultracom cxi / cx / hxi / sxi / Ultrapower sxFan unable to attain ignition speed 
F9Flexicom cx / hx / sx / hxi / Ultracom cxi / cx / hxi / sxiBlocked flow filter, fault with water pressure sensor or pump 
F11Flexicom cx / hx / sxReturn or flow thermistor fault 
F2Ci range (plus)/ Si rangeFan or APS fault 
F10All BoilersCentral return flow thermistor 
F11All BoilersFault on main board connection 
F12Ci (plus) / cxi / hxi / si / sxi rangeConnection fault between display PCB and main PCB 
F13Ci (plus) / cxi / hxi / si / sxi rangeMain PCB connection fault 
F14Ci (plus) / cxi / hxi / si / sxi rangeCentral heating flow temperature 
F15Ci (plus) / cxi / hxi / si / sxi rangeGas valve stepper motor fault 
F17Ci (plus) / cxi / hxi / si / sxi range / Xtramax HEPower supply less than required 170 volts 
F19Ci (plus) / cxi / hxi / si / sxi range / Xtramax HECentral heating thermistor unplugged 
F20Ci (plus) / cxi / hxi / si / sxi range / Xtramax HESoftware incompatibility 
F24cxi / hxi / sxi range / Flexicom cxCentral heating return temperature is higher than 90 degrees. 
 Compact e/sNo C/HCheck DHW microswitch to ensure DHW demand LED is lit.
 Compact e/sNo C/H, but the boiler is firingCheck diverter cartridge and motor
 Compact e/sThe boiler locks out within 10 seconds.Check pump proving switch, overheat state, and air pressure switch.
 Compact e/sPoor burner pressureCheck burner pressure and ignition electrode adjustment posts on PCB
Temperature 30 flashingBetacom CThe central heating thermistor has a fault 
Temperature 40 flashingBetacom CFault on Domestic Hot Water Thermistor 
Temperature 50 flashingBetacom CFault on the outside sensor 
Temperature 60 flashingBetacom CLow system pressure 
Temperature 70 flashingBetacom CFault on APS 
Temperature 80 flashingBetacom COverheat open circuit 
Temperature 90 flashingBetacom CGas or flame failure 
No DHWCompact e/sDHW is inactiveCheck DHW microswitch
F70Betacom, Ultracom2 cxi/sxi/35The user interface is incompatible with the main boardThe user interface needs to be changed
F72 F84Betacom, Ultracom2 cxi/sxi/35The permanent temperature difference between return and heating flow sensors has a fault. 
F73 F74Betacom, Ultracom2 cxi/sxi/35Heating circuit pressure sensor fault 
F76 & F83Betacom, Ultracom2 cxi/sxi/35Fault with thermal fuse 
F85Betacom, Ultracom2 cxi/sxi/35Underfloor heating contact fault 
ERR F12 F18All BoilersUser interface fault 
F00, F10, F7Betacom, Ultracom2 cxi/sxi/35An issue with the flow heating temperature sensor 
F01 F11Betacom, Ultracom2 cxi/sxi/35Return heating temperature sensor fault 
F20Betacom, Ultracom2 cxi/sxi/35Overheating fault 
F9 F22Betacom, Ultracom2 cxi/sxi/hxi/35, Flexicom cx/hx/sxIgnition temperature rise too slow or Low water pressure 
F26 F7Betacom, Ultracom2 cxi/sxi/35Gas valve fault 
F27 F16Betacom, Ultracom2 cxi/sxi/35/CI/hxi, Xtramax HEFlame detection fault 
F28 F1 F4All boilersIgnition fault 
F29Betacom, Ultracom2 cxi/sxi/35Loss of flame during operation 
F32Betacom, Ultracom2 cxi/sxi/35Incorrect air pressure 
F49Betacom, Ultracom2 cxi/sxi/35EBUS voltage fault 
F61 F62 F63 F64 F65 F67Betacom, Ultracom2 cxi/sxi/35Fault in the main board 
F68Betacom, Ultracom2 cxi/sxi/35Fluctuation of flame signal 
Yellow LED onBetacomFlame is present on the burner 
Green LED OnBetacomThe boiler is ready for operation 
Green LED offBetacomThere is no power to the boilerCheck the power connection to the boiler and that the right fuse is connected on the PCB.
Red LED onBetacomLockout due to low water pressureIncrease water pressure to 1.5 and reset the boiler
Red LED flashingBetacomOverheatingCheck stats on overheating
Yellow LED flashingBetacomThe domestic hot water temperature is offTurn the DHW control knob to the temperature range. Turn the central heating temperature control knob into reset position and wait for 30 seconds before switching to temperate or summer position.


These Glow Worm boiler error codes can appear when the pipe is frozen. Frozen pipes tend to occur during the colder months, especially if the pipes are run outdoors.

You can fix this issue yourself; however, if you are not confident enough or do not have the required skills to fix the boiler problem indicated by the fault code, whether it’s a water pressure sensor fault, heat exchanger, or short circuit, you will need to contact a licensed boiler repair or Gas Safe engineer.

With this article on Glow Worm error codes, you should have no problem ascertaining what fault your combi boiler has at that very moment. Understanding the Glow Worm error codes can save you quite some time troubleshooting.

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