Glow Worm Error Codes, Faults & Fixes

James Elston
Written by James Elston
Updated on 2nd January 2024
Posted on 1st January 2024
Glow Worm Error Codes, Faults & Fixes

Glow Worm boiler error codes & fault code guide for 2024

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.

If you are experiencing one or more of these Glow Worm error codes and your boiler is over 10 years old then it may be time to consider a new boiler.

If your boiler is less than 10 years old then we strongly suggest getting in touch with Glow worm or a Gas Safe registered heating engineer when you get your Glow Worm boiler service to discuss what the best option is moving forward

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    Glow Worm Boiler Error Codes

    See our list of Glow Worm error codes to help you quickly diagnose any issues with your boiler. Be aware of common problems you can fix yourself too like low boiler pressure or a frozen boiler condensate pipe, which can save you money on expensive callouts!

    Other things that also may not crop up but still cause you issues are things like a boiler timer not working, which could cost you money in the long run by turning your boiler on when you don’t need it!


    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 – Possible frozen condensate pipe


    Loss of flame – Possible frozen condensate pipe


    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. A frozen condensate pipe is classed as a blockage and will stop your boiler from working and possibly show one of the following error codes:

    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.

    Written by
    James Elston
    James Elston Director Of Boiler Central
    Posted on: 1st January 2024

    James Elston is our resident boiler replacement and heating expert here at Boiler Central. With over 20 years experience in the boiler installation industry, James ensures that he knows everything there is about our Gas Safe boiler installations, energy saving and home heating solutions. This can be from simply procuring the latest best combi boilers, to reviewing and ensuring that Boiler Central maintains the highest standards across our boiler installation company.

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