Boiler fault codes
Glow-worm Boiler Fault Codes Explained
Glow-worm boilers use two code systems. Older models such as the Flexicom, Ultracom, cxi and sxi show plain codes like F1 and F9. Newer ranges such as Energy and Ultracom2 show codes with a dot, like F.22 and F.28, and the same number can mean something different. Check which you have before looking it up.
Why do Glow-worm codes look different on different boilers?
Glow-worm is part of the same group as Vaillant, and its newer boilers use Vaillant-style controls. On an Energy or Ultracom2 boiler, F.22 means low water pressure, F.28 means the boiler failed to light and F.29 means the flame went out while it was running. F.01 on those boilers is a return temperature sensor fault.
Older ranges use a shorter list. On a Flexicom cx, for example, F1 is an ignition fault and F9 is a water pressure sensor, flow filter or pump fault. So if your display shows F1 and you look up F.01 by mistake, you will be chasing a sensor when the real problem is ignition. The model name is printed on the front of the boiler.
Some older Glow-worm boilers have no code display at all. The first Betacom used coloured lights instead: Glow-worm’s table for that range lists a steady red light as a low water pressure lockout, cleared by bringing the pressure back up and resetting, and a flashing red light as either an overheat or the hot water knob left in its service position.
Which Glow-worm codes can I deal with myself?
Glow-worm’s homeowner advice covers two faults you can often clear yourself. For anything else, it says to contact an installer rather than attempt a fix.
- Water pressure, F9 on older boilers or F.22 on newer ones: top up through the filling loop to 1 to 1.5 bar, then reset. The Glow-worm pressure guide walks through it.
- Ignition, F1 on older boilers or F.28 and F.29 on newer ones: check a prepayment gas meter has credit and thaw a frozen condensate pipe with warm, not boiling, water, then reset.
- Engineer only: on the Energy range Glow-worm lists F.61 as a gas valve control fault, F.64 as an electronics or sensor fault and F.67 as an implausible flame signal. Those, and any code pointing at a sensor, the fan or overheating, need testing inside the casing.
Reset once, not repeatedly. A code that returns straight away is telling you the cause is still there. If you smell gas, open the windows, turn the gas off at the meter if it is safe to, keep off the switches and call 0800 111 999 from outside before anything else.
When does a Glow-worm code need a visit?
Call an engineer if the same code returns after one reset, if you are topping up the pressure every few days, or if the code is not one of the two above. On an older boiler the code narrows the search but does not settle it: Glow-worm’s own F9 entry for the Flexicom cx names three possible parts.
Gas work is carried out by Gas Safe registered engineers. The visit starts with the £60 call-out and the repair price is agreed with you on site before any work starts. Book through Glow-worm boiler repair, day or night.
| Code | What it means | Can you clear it yourself? |
|---|---|---|
| F1 | Ignition fault: no flame detected, boiler locked out (older models) | Yes, once; call if it returns |
| F3 | Fan cannot reach ignition speed (older models) | No, call an engineer |
| F5 | Overheat fault (older models) | No, call an engineer |
| F6 | Central heating flow temperature sensor fault (older models) | No, call an engineer |
| F9 | Water pressure fault (older models) | Yes, once; call if it returns |
| F.01 | Return temperature sensor fault (Energy, Ultracom2) | No, call an engineer |
| F.22 | Low water pressure (Energy, Ultracom2) | Yes, once; call if it returns |
| F.28 | The boiler failed to light (Energy, Ultracom2) | Yes, once; call if it returns |
| F.29 | Flame went out and would not relight (Energy, Ultracom2) | Yes, once; call if it returns |
| F.61 | Gas valve control fault (Energy, Ultracom2) | No, call an engineer |
| F.64 | Electronics or sensor fault on the main board (Energy) | No, call an engineer |
| F.67 | Implausible flame signal: electronics fault (Energy) | No, call an engineer |
| F.75 | No pressure rise when the pump starts (Energy) | Yes, once; call if it returns |
Glow-worm codes explained
- F1On older Glow-worm boilers F1 is an ignition fault: the boiler tried to light, never detected a flame, and locked out. On the newer Energy and Ultracom2 ranges the similar-looking F.01 or F01 means something else, a return temperature sensor fault.
- F9On older Glow-worm boilers F9 is a water pressure fault. Most often the system simply needs repressurising, while Glow-worm’s engineer tables list a faulty water pressure sensor, a blocked flow filter or a pump fault.
Questions people ask
What does F4 mean on an older Glow-worm boiler?
Glow-worm’s trade tables for the Flexicom, Ultracom, cxi, sxi and similar older ranges list F4, like F1, as an ignition fault. Run the same gas supply and condensate checks as for F1, reset once, and call an engineer if it returns.
Where is the reset button on a Glow-worm boiler?
On the front control panel. Its exact position and symbol depend on the model, so check your user instructions. Press it once and wait for the boiler to try again.