Lockout or ignition failure (flame with a cross)
The boiler tried to light its burner, failed several times in a row and has locked itself out for safety. It stays off until someone resets it.
What the manual says to do
First check what the manuals list: are other gas appliances working, is there credit on a prepayment meter, is the gas turned on? Then reset once (see the reset page). Ideal’s display says: “Check other gas appliances work. Restart boiler. If fault persists, contact installer.” Vaillant allows three fault-clearance attempts before you consult a competent person.
Only your boiler’s own manual says exactly what a symbol means on your model. The manuals let the householder reset a fault once, top up the pressure through the filling loop and change the settings; anything else on a gas boiler is a job for a qualified heating engineer (Gas Safe registered in the UK), as the manuals themselves say.
If you smell gas
Baxi’s manual (Baxi Compact range (quick guide 7849761)): “If you smell gas Call the National Gas Emergency free on 0800 111 999. If you think you have a gas leak you need to act quickly. Open doors and windows. Turn off gas at meter (unless the meter is in a cellar or basement). Don’t use electric switches or naked flames.”
Quick start guide to your boiler, 7849761 Baxi Compact quick guide user instructions (PDF) Checked 2026-09-27. The number is the UK’s National Gas Emergency Service; elsewhere, call your own gas emergency number.
What it does not mean
It does not mean there is a gas leak, and it is not something to reset over and over: a lockout that returns needs an engineer. If you do smell gas, do not press anything on the boiler; follow the emergency steps below.
- What it looks like
- A flame crossed through or with a line across it, a flame beside an R, or words such as ‘Ignition Lockout’ or a code like L 01 on the display.
- Names used
- Ignition Lockout (Ideal); Flame failure (Baxi); Ignition fault F.28 (Vaillant); Burner fault, burner locked out (Viessmann)
Where makers differ
Vaillant locks out after three unsuccessful ignition attempts and shows F.28; Ideal after five, shown as ‘Ignition Lockout’ or an L and a number; Baxi shows a flame-failure symbol with its reset symbol; Viessmann shows a burner fault and says the burner “is locked out”.
Other symbols with the same shapes
Sources
No public standard defines this boiler symbol, so its meaning is taken from the manuals of 4 different maker groups (Vaillant, Ideal Heating, Baxi, Viessmann), each fetched and read on the date shown:
- Vaillant, ecoTEC plus VU, VUW, VUI ..6/5-5: Operating instructions ecoTEC plus, 0020245033_02 (26.05.2021) GB, IE (PDF) — Troubleshooting: “After three unsuccessful attempts to ignite the flame, the product switches to fault mode (fault message: F.28)”; three fault clearance attempts, then consult a competent person. Checked 2026-09-27.
- Ideal Heating, Logic Max Combi2 C24, C30, C35: Logic Max Combi2 user guide, UIN 228290 A06 (October 2022) (PDF) — “If the boiler fails to light after five attempts the following fault messages will be displayed: Ignition Lockout — 1 Check other gas appliances work. 2 Restart boiler. 3 If fault persists, contact installer.” Checked 2026-09-27.
- Ideal Heating, Logic Combi2 C24, C30, C35: Logic Combi2 user guide, UIN 237664 A01 (10/2023) (PDF) — Display codes: “Boiler is in Lockout for a specific error. Display will show a number after the ‘L’ to indicate which error is detected.” Checked 2026-09-27.
- Baxi, Baxi 800 Combi: Baxi 800 Combi user guide, 7728204-01 (PDF) — Start-up flow chart: flame failure symbol beside the reset symbol, “Press the Reset Button (e.g. press and hold for 5 seconds)”, and if it does not reset, contact your installer or service engineer. Checked 2026-09-27.
- Baxi, Baxi Compact range (quick guide 7849761): Quick start guide to your boiler, 7849761 Baxi Compact quick guide user instructions (PDF) — “If you smell gas — Call the National Gas Emergency free on 0800 111 999 … Open doors and windows. Turn off gas at meter … Don’t use electric switches or naked flames.” Checked 2026-09-27.
- Viessmann, Vitodens 100-W/111-W/111-F/141-F (black/white screen): Operating instructions for the system user, 6167584 GB (12/2020) (PDF) — “Burner fault … A fault has caused the burner to lock out. You can reset it.”; make a note of the fault number; notify your heating contractor if the fault recurs. Checked 2026-09-27.
Written in our own words; quotations are the makers’ wording.