Ideal Boiler Fault Codes: F1, F2, L2 and What to Do

Updated July 2026 · Emergency Plumber Chelsea

Ideal boilers use two kinds of code. An F code is a fault the boiler has detected and may recover from once the condition clears. An L code is a lockout: the boiler has shut itself down for safety and will stay off until someone resets it. That difference matters. An F1 will usually clear by itself as soon as the pressure is back up, while an L2 needs a reset and, if it keeps coming back, a proper diagnosis. Codes can vary slightly between models and generations, so check the one on your display against the manual, which is often stored behind the front flap or available from Ideal with the model name on the data plate.

F1 is low system pressure. Look at the pressure gauge on the front of the boiler. With the heating cold it should normally read around 1 to 1.5 bar. If it has fallen well below 1, top it up using the filling loop, the flexible hose or key-operated valve underneath the boiler, following the steps in your manual. Open the valves slowly, watch the gauge, and close them firmly once you reach the right pressure. The F1 should clear on its own. If you need to repeat this every few days or weeks, water is leaving the system, through a leak, the pressure relief valve or a failed expansion vessel. Our guide to why a boiler keeps losing pressure explains how to narrow that down.

A word of warning on F1: do not overfill. If you push the pressure up to 2.5 or 3 bar with the system cold, it will rise further when the boiler heats up, and the pressure relief valve may open and dump water through the pipe on the outside wall. Then you are back to F1. If you have already gone too high, our guide on boiler pressure that is too high shows how to bring it down safely.

F2 means flame loss. The boiler lit, then lost the flame during operation. Start with the gas supply: check the hob or any other gas appliance, and if you are on a prepayment meter, check the credit. If the gas is fine and it is cold outside, check the condensate pipe, the thin plastic pipe that runs from the boiler to a drain, often outside. When it freezes, condensate backs up and the burner shuts down. Warm water poured along the pipe, never boiling, usually thaws it, and our frozen condensate pipe guide covers the steps. If neither explains it, F2 can point to a flue problem, a faulty flame sensing electrode or a gas valve issue, all of which are Gas Safe work.

L2 is an ignition lockout. The boiler has made several attempts to light, detected no flame each time, and locked out. It is the Ideal equivalent of the ignition faults other brands report, and the first checks are the same as for F2: gas supply, prepayment credit and the condensate pipe. Once you have checked those, reset the boiler. On many Ideal models you turn the mode knob to the reset position and hold it for a few seconds; on others there is a dedicated reset button. If the boiler fires and keeps running, keep an eye on it. If it goes straight back to L2, stop resetting. Repeated L2 lockouts usually mean a worn ignition electrode, a faulty ignition lead or generator, a gas valve fault or a blocked flue or air intake, and those need an engineer to open the combustion side of the boiler.

A few other codes come up regularly. F3 generally indicates a fan fault, and F4 and F5 a problem with the flow or return temperature sensors. L1 is usually a circulation or overheat lockout, pointing to a stuck pump, closed valves or sludge restricting flow. These are not codes you can fix with a top-up or a reset; the boiler has found a component that is not behaving and it needs testing. If you are not sure which code you are looking at, take a photo of the display and send it to us or read it out when you call.

If you searched for an F1 boiler fault and do not have an Ideal, check the badge on the front. Different manufacturers use the same letters for different things. On many older Glow-worm models, for example, F1 relates to ignition rather than pressure, and Baxi and Worcester use their own code systems altogether. Our Worcester fault code guide covers EA 227 and the flashing blue light, and our Baxi fault code guide covers E133, E119 and the E1 display. On a Glow-worm, our guide to Glow-worm boiler pressure explains the F22 low pressure code.

Some things are never worth trying. Do not take the casing off, do not try to clean the electrode yourself, and do not keep pressing reset. Every failed ignition means unburned gas has been released, and most boilers limit how many resets they will accept before a longer lockout. If you smell gas at any stage, leave the property, avoid switches, and call the National Gas Emergency Service on 0800 111 999 from outside.

Most Ideal lockouts come down to a handful of causes: a worn electrode, a sludged heat exchanger in an older system, a condensate trap that has not been cleaned, or pressure problems from a tired expansion vessel. An annual boiler service catches most of these before the first cold spell. When a fault does happen, our boiler repair service sends Gas Safe registered engineers across SW3, SW10, Knightsbridge, South Kensington and Fulham. Call Emergency Plumber Chelsea on 020 3002 6667 with the fault code and model. There is no call-out fee on jobs over 3 hours.

Quick tips

• F codes can clear by themselves once the problem is fixed; L codes are lockouts that need a reset.
• For F1, top up to around 1 to 1.5 bar with the system cold, then close the filling loop valves firmly.
• For F2 or L2, check the hob and the prepayment meter credit before anything else.
• In frosty weather, check the condensate pipe; thaw it with warm water, never boiling.
• If L2 returns straight after a reset, stop and book a Gas Safe engineer.

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