Glow-worm F1 Fault Code: The Burner Failed to Light

What does F1 mean on a Glow-worm boiler?

Glow-worm’s own trade fault tables list F1 as “ignition fault” across its older ranges: the Flexicom cx, hx and sx, the Ultracom cx, cxi, hxi and sxi, and the CI, cxi, SI, sxi, hxi and Xtramax HE models. When the boiler asks for heat it opens the gas valve and sparks the electrode. If the flame sensing electrode does not detect a flame within the safety time, the control board shuts the gas off and holds the boiler in lockout until someone resets it.

Check the display before going further. Newer Glow-worm boilers, including the Energy and Ultracom2 ranges, use two-digit Vaillant-style codes, shown as F.28 or F28. On those, ignition failure is F28 and flame loss while running is F29. F01 on those boilers is a return temperature sensor fault, which is a different job. The same older tables also list F4 as an ignition fault, so treat F4 exactly as you would F1.

What should I check before I reset it?

Start with the gas supply, because it is the cause most often outside the boiler. Turn on a gas hob. If it will not light either, the problem is the supply, not the boiler. On a prepayment meter, top up and follow the meter’s restart steps, which usually include accepting emergency credit or pressing a button to reopen the valve. If the meter has credit and nothing lights, contact your gas supplier. If you smell gas at any point, open windows, turn the gas off at the meter if safe, avoid switches and call 0800 111 999 from outside.

Next, the condensate pipe. A condensing boiler drains acidic water through a white or grey plastic pipe, often to a drain outside. When that pipe freezes, the water backs up into the boiler and it will not light. Glow-worm’s own homeowner advice names a frozen condensate pipe as a reason a boiler will not ignite, and in a cold snap ice is the usual blockage. Pour warm water along the frozen section, never boiling, then reset.

Press the reset button once. If the boiler lights and stays lit, keep an eye on it for the rest of the day. If it locks out again straight away, the cause is inside the casing and that is not a householder check.

Do not keep pressing reset. Each press runs the whole ignition sequence again, gas valve included, and the lockout exists to stop a boiler that cannot prove a flame from trying over and over.

Why does F1 keep coming back?

When the gas supply and condensate are fine, an engineer works through the ignition sequence in order. First, is there a spark? A worn or badly gapped ignition electrode, or a failed ignition lead, gives weak or no spark. Second, does gas arrive at the burner? The engineer checks the inlet working pressure at the boiler, then whether the gas valve opens when the board tells it to. Third, is the flame seen? A dirty or eroded flame sensing electrode can let the boiler light briefly and then drop out, which looks like F1 to you.

Beyond those, a partly blocked flue or air intake, a condensate trap full of debris, or a poor earth can all stop ignition. The control board itself is the last thing to condemn, after everything it controls has been tested.

Does F1 need an emergency visit?

If you have no heating or hot water and the checks above have not worked, yes, particularly in cold weather or with someone vulnerable in the house. An electrode replacement is a short job. A gas valve or control board costs more and may need ordering, so the engineer will make the boiler safe and tell you where it stands. 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. You can book a Glow-worm boiler repair at any hour, or read how an ignition lockout works on other makes.