Glow-worm [F1] fault codewhat it means and how to fix it

Two boilers, one number, and the display tells you which you have. If yours is an Ultracom cxi, hxi or sxi, a Flexicom cx, hx or sx or an Ultrapower sxi — a flashing F and a single digit on a small LCD — Glow-worm's user guides define F1 in one line: "Boiler has attempted to light 5 times and failed on all occasions. Press the reset button. If the fault persists, contact your Installation/Servicing company or Glow-worm." The trade tables for those ranges, and for the 24CI, 18SI, 30ci Plus, Xtramax HE and Ultracom cx before them, all list F1 as "ignition fault"; the CI-era boilers showed it as 01 with the letter F and a flashing red light.

The same guides give the householder two things to check around it: the switching-on section says to "check that the water and gas isolating valves on the appliance are open", and the condensate section says the boiler stops if the drain is blocked and that an ice blockage can be released "by the use of warm cloths on the pipe", after which "the boiler should then restart". Glow-worm's current homeowner page gives the same checks, plus prepayment credit, for the modern equivalent F.28.

If instead your boiler is an Energy, Ultimate3, Easicom, Betacom3 or 4 or Compact showing F.01 with a stop, or an Ultracom2 or Betacom2 showing F01, the code has nothing to do with ignition: it is "Fault: Return temperature sensor", the return NTC unplugged, its plug loose on the board, a break in the harness or the sensor itself failed, and that half of the page is an engineer's job. The five attempts of the old F1 against the three of the new F.28 is a genuine difference between the generations, not a transcription slip.

1. 1

   Identify the display. A single-digit F1 with a flashing F on an Ultracom, Flexicom or Ultrapower is the ignition lockout and the steps below apply. F.01 with a stop, or F01 on an Ultracom2 or Betacom2, is the return sensor — skip to calling an engineer.

2. 2

   Check the gas supply: does the hob light, is the meter in credit, is the gas isolating valve under the boiler open? The guides ask for it open before switching on, and a lockout after five attempts with no gas is not a boiler fault.

3. 3

   Trace the condensate pipe outside and free any frozen section with warm cloths, which is the method the Flexicom and Ultracom guides give. Warm, not boiling — the Betacom2 guide adds that warning for the same job.

4. 4

   Press the reset button on the fascia once. The guide says the boiler should return to operation if the supply or the pipe was the problem; if F1 returns, leave it switched off and call your installer or a Gas Safe registered engineer, because five more attempts have already been made for you.