What F1 is
The boiler has attempted to light and has not confirmed a flame, so it has locked out. Glow-worm's trade fault-finding table for the Betacom A range gives F1 simply as "Ignition fault". Glow-worm's homeowner guidance is more specific about causes: it names F28 and F29 as the current codes for this, says F1 is the equivalent on older appliances, and puts the usual causes as the gas supply, including a prepayment meter out of credit, or a condensate pipe that is frozen or blocked.
Related codes on the same range fill in the picture. The Energy range table gives F.28 as "Fault: Ignition unsuccessful when starting up" and F.29 as "Fault: Flame loss". Nothing in any of it concerns water escaping from the system.
Three things you can check
- Gas. Try the hob or another gas appliance. If nothing gas-powered works, the fault is upstream of the boiler. On a prepayment meter, check the credit, because an empty meter produces this code exactly.
- The condensate pipe. Find the white or grey plastic pipe leaving the base of the boiler and running outside. If it is frozen, condensate backs up and the boiler shuts down. Switch the boiler and its electrical supply off, warm the frozen section with a hot water bottle or heat pack rather than boiling water, then restart.
- One reset. After clearing an obvious cause, reset once. If it locks out again, stop and call an engineer. Repeated resets put the appliance through failed ignition cycles and wear the ignition and flame-sensing electrodes.
Glow-worm's own advice is blunt on the rest: if a fault code appears and you are unsure, contact an installer and do not attempt to fix it yourself.
When it becomes a Gas Safe job
If gas is present at other appliances and the condensate pipe is clear, everything left is inside the boiler: the ignition electrode, the flame-sensing electrode, their leads, the gas valve, the fan, or the PCB. Glow-worm's fault tables point at gas meter or gas pressure problems for F.28, and at interrupted gas supply, flue gas recirculation and incorrect earthing for F.29.
All of that is gas work, and in the UK anyone working on a gas appliance has to be on the Gas Safe Register. You can check an engineer's registration and the specific appliance types they are qualified for on the register's site before they touch anything.
If you smell gas, do not reset the boiler. Shut the gas off at the emergency control valve by the meter, open windows, keep away from switches and flames, and call the National Gas Emergency Service on the number published by Gas Safe Register.
The case where a leak is involved
A leak does not cause F1, but a leak in the wrong place can produce it. Water tracking into the boiler case, from a flue seal, a corroded internal joint or a pipe above the appliance, can reach the ignition or flame-sensing electrode and its connections. A wet electrode will not spark reliably or will not read a flame that is there, and the boiler locks out.
You diagnose that by looking, not by the code. Staining or corrosion under the case, a white or green bloom on pipework, drips on the floor beneath the boiler, or a tide mark on the wall behind it are the signs. An engineer who opens the case will see it in seconds.
The other connection is simpler and much more common: a boiler that shows F1 in the morning and F22 by the weekend has two separate problems, and only the second one is ours. F22 is the low water pressure code, and that is the one that points at water leaving the system.
What the engineer should check, and in what order
Gas pressure at the appliance comes first, standing and working, because a weak supply produces this code with nothing wrong inside the boiler. Then whether the ignition electrode is sparking at all, the gap it is set to, and the condition of its lead. Then flame sensing, since an electrode coated in carbon cannot read a flame that is burning in front of it. Then the gas valve and the fan. The PCB is the last item on that list rather than the first, and a quote that opens with a new board and none of the earlier checks is a quote to replace the dearest component on a guess.
Why F1 returns every winter
If the fault arrives with the first hard frost each year, the condensate pipe is the problem rather than the boiler. The usual reasons are an external run that is too long, a diameter too small for that run, too little fall so condensate stands in the pipe, or an outlet in a wind-exposed spot. Thawing it gets the heating back on. Re-routing the pipe internally where the layout allows, increasing the diameter of the external section, or lagging it properly is what stops it happening again, and that is ordinary plumbing rather than gas work.
What not to pay for
Do not book leak detection for an F1 on its own. There is nothing for a leak engineer to find, and any firm that sells you a detection survey off the back of an ignition code is charging you to look for a fault the boiler has not reported.
Do not accept a replacement boiler as the first answer either. An electrode, a lead, a gas valve or a fan is a component repair on an appliance that is otherwise sound. Have the fault diagnosed before anyone prices a new one.
If the same engineer finds the system is also losing pressure, that half is ours. We charge a fixed hourly rate, agreed before we attend, with no find, no fee on the detection, and we carry out the repair and the reinstatement rather than handing over a report. The cross-brand list of codes that really do mean water loss is here.
