Flame: burner on
The burner is lit: the boiler is burning gas right now, to heat the radiators or tap water.
What the manual says to do
Nothing to do: it comes and goes as the boiler fires and adjusts its output. If it never lights when you need heat or hot water, check the gas supply (other gas appliances, credit on a prepayment meter) as the manuals list, then see the reset page. If you smell gas, switch nothing on or off and follow the emergency steps below.
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
Worcester Bosch’s manual (Greenstar 4000 combi (GR4700iW C)): “If you smell gas, observe the following rules: … Do not operate any electrical switches or unplug any equipment. … Turn off the gas at the meter or regulator. Open windows and doors. Warn your neighbours and leave the building. … Move well away from the building: call the National Gas Emergency Service on 0800 111 999.”
Greenstar 4000 user instructions, 6 720 891 170 (2020/09) UK/IE (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 is not a fault or a warning, and it is not a pilot light: a modern boiler lights its burner only when heat or hot water is asked for. A flame that stays out does not by itself mean a fault; the boiler may simply have no demand.
- What it looks like
- A single flame, lit on the display or as a separate light. Vaillant’s current display also shows the burner’s output as a bar in five steps.
- Names used
- Burner display (Worcester Bosch); Burner on (Vaillant); Burner lit (Baxi); Burner on indicator (Ideal); Burner status active (Viessmann)
Where makers differ
Worcester Bosch calls it the burner display (“Illuminates when the burner is alight”); Baxi “Burner lit”; Ideal the burner on indicator; Viessmann “Burner status active”. Vaillant’s 2021 manual lists ‘Burner on’; its 2023 manual shows the current burner modulation rate in five levels.
Other symbols with the same shapes
Sources
No public standard defines this boiler symbol, so its meaning is taken from the manuals of 5 different maker groups (Worcester Bosch, Vaillant, Baxi, Ideal Heating, Viessmann), each fetched and read on the date shown:
- Worcester Bosch, Greenstar 4000 combi (GR4700iW C): Greenstar 4000 user instructions, 6 720 891 170 (2020/09) UK/IE (PDF) — Control panel overview: “Burner display: Illuminates when the burner is alight.” Safety chapter: what to do if you smell gas, National Gas Emergency Service 0800 111 999. Checked 2026-09-27.
- Vaillant, ecoTEC plus VU, VUW, VUI ..6/5-5: Operating instructions ecoTEC plus, 0020245033_02 (26.05.2021) GB, IE (PDF) — Displayed symbols: “Burner operating correctly — Burner on”. Checked 2026-09-27.
- Vaillant, ecoTEC plus VU../VUW../VUI.. (current range): Operating instructions ecoTEC plus, 0020308119_03 (28.11.2023) (PDF) — Displayed symbols: “Current burner modulation rate (display in five levels)”. 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) — Display symbols: “Burner lit”; “If you smell gas — Call the National Gas Emergency free on 0800 111 999”. Checked 2026-09-27.
- Ideal Heating, Logic Max Combi2 C24, C30, C35: Logic Max Combi2 user guide, UIN 228290 A06 (October 2022) (PDF) — “During normal operation the burner on symbol (E) will remain illuminated when the burner is lit.” 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) — Symbols in function area A: “Burner status active”. Checked 2026-09-27.
Written in our own words; quotations are the makers’ wording.