L2 Boiler Fault Code: What It Means on Every Brand

L2 is a lockout code with two quite different stories depending on what you own. On Ideal boilers (the Logic and Vogue especially) and on Keston, L2 is the flame-loss lockout — the boiler lit, or tried to, and lost its flame — and it is the single most common Ideal code searched for in winter, almost always because of a frozen condensate pipe or a gas-supply interruption. On the Grant Aerona³ heat pump, L2 is a different animal entirely: a controller-side fault with nothing to do with gas. Check which appliance you have before reading on.

Up to: Lockout — engineer likely 3 brands use this code Meaning differs by brand

Which brand is your boiler?

The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.

Brand	What L2 means	Severity	DIY?
GGrant	The L2 fault code on the Grant Aerona³ air source heat pump indicates that the control system has detected a problem with the inlet (return) water temperature sensor. Full guide →	Engineer may be needed	No
IIdeal	L2 on an Ideal boiler is a flame-loss lockout: the boiler tried to light — or lit and then lost the flame — and could not detect a stable flame, so it shut down for safety. Full guide →	Lockout — engineer likely	Some checks
KKeston	The L2 fault code on Keston boilers indicates a flame loss lockout — the boiler's flame detection system has confirmed that the burner either failed to ignite successfully or cut out… Full guide →	Lockout — engineer likely	Some checks

L2 brand by brand

Grant L2

The L2 fault code on the Grant Aerona³ air source heat pump indicates that the control system has detected a problem with the inlet (return) water temperature sensor. This NTC thermistor sits on the water circuit returning to the heat pump and feeds continuous temperature data to the main PCB. When the reading falls outside the expected resistance-temperature curve — or disappears entirely — the heat pump raises the L2 alert and may stop operating to protect the system. The code appears on the Aerona Remote Controller LCD alongside a warning icon and a flashing red LED, and a matching two-digit code is shown on the Terminal PCB LED display inside the outdoor unit.

Causes, fixes & costs for Grant L2 → · All Grant codes

Ideal L2

L2 on an Ideal boiler is a flame-loss lockout: the boiler tried to light — or lit and then lost the flame — and could not detect a stable flame, so it shut down for safety. It is the most-searched Ideal code by a wide margin, and it spikes every cold snap because the commonest cause on the Logic and Vogue ranges is a frozen condensate pipe. The other frequent cause is a gas supply that has stopped: an empty prepayment meter, a closed emergency control valve, or a network interruption. L2 is closely related to F2 (the flame-loss fault that precedes it) — F2 is the fault, L2 is the lockout the boiler enters after repeated F2s. Check gas and condensate, reset once, and call a Gas Safe registered engineer if it comes back.

Causes, fixes & costs for Ideal L2 → · All Ideal codes

Keston L2

The L2 fault code on Keston boilers indicates a flame loss lockout — the boiler's flame detection system has confirmed that the burner either failed to ignite successfully or cut out during operation. As a safety precaution, the boiler shuts itself down completely and will not restart until the underlying fault is resolved and the boiler is manually reset using the dedicated reset button (simply switching the boiler off and back on at the mains will not clear a lockout on Keston models). On Keston Combi and System boilers, you may also see this displayed as F2 rather than L2. Keston Heat boilers may instead show the message 'Check Condense' when a frozen or blocked condensate pipe is the trigger. Because Keston boilers use a twin-flue design with a modulating pump, they are considered more complex than average, and not all Gas Safe engineers are equally familiar with them — always check that your engineer has Keston experience.

Causes, fixes & costs for Keston L2 → · All Keston codes

Frequently asked questions

Is the L2 fault code the same on every boiler?

No. L2 means different things on different brands — see the table above. Always identify your boiler's brand (it is printed on the front casing) before acting on any advice about the code.

Can I fix a L2 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. Where the code is a simple pressure or reset condition, that may be all it needs. Never open the boiler casing yourself.

Who should I call about a L2 fault?

For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. For heat pumps, an MCS or F-Gas qualified heat pump engineer. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.

General guidance only — not a substitute for professional advice, and not certified by a registered engineer. Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.