What do the lights on my boiler and the numbers on my radiator valve mean?
Find it by its shape. 1. Pick what you see on the boiler’s panel or the radiator valve. 2. Match the drawing. Each of the 14 boiler symbols is backed by the manuals of at least two different maker groups; the 2 radiator-valve pages quote the valve makers’ own setting temperatures.
Tap a shape — the symbols that use it appear here.
Radiator — 2 symbols
Tap — 4 symbols
Tap: hot waterA tap with a drop or a stream of water, sometimes with wavy lines…Eco, comfort or pre-heat: hot water kept readyThe word ‘eco’ on a key or the display, a ‘Preheat’ key, or a tap…Summer mode (hot water only) and winter mode (heating and hot water)Summer: the radiator crossed out or dropped, with the tap still…Tap crossed out: hot water offThe tap symbol with a line or cross through it, or the tap missing…
Flame — 3 symbols
Flame: burner onA single flame, lit on the display or as a separate light.…Reset button (R, Reset, Restart, circular arrow)A button marked R, ‘Reset’ or ‘Restart’, a circular arrow, or on…Lockout or ignition failure (flame with a cross)A flame crossed through or with a line across it, a flame beside…
Gauge, drop or bar — 1 symbol
Arrows, + and − — 2 symbols
Spanner, warning or chimney — 3 symbols
Spanner: service due, or an engineer neededA spanner (wrench), alone or beside a code. Vaillant adds a…Fault symbol (warning, ‘!’, or a code on the display)A warning mark or ‘!’ next to a code: F. and two digits on…Chimney-sweep or flue-gas test modeA symbol for a chimney or flue, or a named key, lit on the display…
Snowflake or ✱ — 2 symbols
Radiator valve head — 2 symbols
Power or lock — 2 symbols
At a glance
- Radiator valve numbers are rough room temperatures. Danfoss RAS-C sensor: ✱ = 8 °C, 1 = 12 °C, 3 = 20 °C, 5 = 28 °C; Honeywell Home (Resideo) VT15 / VTL15: ✱ = 6 °C, 1 = 10 °C, 3 = 20 °C, 5 = 26 °C; IMI Heimeier Thermostatic head K: ✱ = 6 °C, 1 = 12 °C, 3 = 20 °C, 5 = 28 °C. The numbering differs by maker and the result depends on the room. The full table →
- Pressure: about 1 to 1.5 bar cold on most boilers. The ranges differ by model: Vaillant 1.0–2.0 bar, Worcester Bosch 1–1.5 bar, Baxi 1.0–2.5 bar, Ideal 1–2 bar. When and how to top up →
- Reset once, not over and over. Vaillant says to consult a competent person after three unsuccessful fault-clearance attempts; Baxi says a fault shown with the spanner cannot be reset by the user.
- If you smell gas, the manuals say: do not operate electrical switches, turn off the gas at the meter, open doors and windows, leave, and call the National Gas Emergency Service on 0800 111 999 (UK).
- Beyond the manual, call an engineer. Vaillant: “Never attempt to carry out maintenance work or repairs on your product yourself.” Anything past a reset, a top-up or a setting is a job for a qualified heating engineer.
What this page cannot do
- It cannot identify your boiler or say exactly what a light does on your model: makers draw and place these symbols differently, and even one maker’s models differ. It explains what a drawing means on the makes cited (Baxi, Danfoss, Drayton, Honeywell Home (Resideo), Ideal Heating, IMI Heimeier, Vaillant, Viessmann, Worcester Bosch); your boiler’s manual is the authority.
- Boiler error codes (such as F.28, E133, L 02 or 214) are out of scope: each maker numbers its faults differently, per model, so they need the maker’s own fault table or an engineer.
- It gives no repair steps beyond what the manuals give the householder — resetting once, topping up the pressure, changing a setting. Anything else is a job for a qualified heating engineer, as the manuals say.
- It does not cover heat-pump panels (defrost, backup heater, hot-water boost) yet, or smart thermostats and programmers, which have their own manuals. It has not read the paid IEC 60417 symbol database: we found no public source showing these boiler icons in it, so every meaning here comes from makers’ documents.
Sources
Every document is a maker’s own user manual, operating instructions, data sheet or advice page, fetched and read on the date shown. Makers in the same group count as one when a symbol needs two independent sources: Vaillant and Glow-worm, Worcester Bosch and Buderus, Baxi and Potterton.
- Worcester Bosch (Worcester Bosch / Buderus group), Greenstar 2000 combi (GR2301iW): Greenstar 2000 user instructions, 6 721 839 343 (2023/04) UK/IE (PDF) Checked 2026-09-27.
- Worcester Bosch (Worcester Bosch / Buderus group), Greenstar 4000 combi (GR4700iW C): Greenstar 4000 user instructions, 6 720 891 170 (2020/09) UK/IE (PDF) Checked 2026-09-27.
- Worcester Bosch (Worcester Bosch / Buderus group), Greenstar 24/28/30 combi: Greenstar 24/28/30 combi user instructions, 6 720 811 923 (2014/07) UK (PDF) Checked 2026-09-27.
- Vaillant (Vaillant / Glow-worm group), ecoTEC plus VU, VUW, VUI ..6/5-5: Operating instructions ecoTEC plus, 0020245033_02 (26.05.2021) GB, IE (PDF) Checked 2026-09-27.
- Vaillant (Vaillant / Glow-worm group), ecoTEC plus VU../VUW../VUI.. (current range): Operating instructions ecoTEC plus, 0020308119_03 (28.11.2023) (PDF) Checked 2026-09-27.
- Vaillant (Vaillant / Glow-worm group), Vaillant boilers in general: How to reset a boiler (Vaillant UK advice page) Checked 2026-09-27.
- Baxi (Baxi / Potterton group), Baxi 800 Combi: Baxi 800 Combi user guide, 7728204-01 (PDF) Checked 2026-09-27.
- Baxi (Baxi / Potterton group), Baxi Compact range (quick guide 7849761): Quick start guide to your boiler, 7849761 Baxi Compact quick guide user instructions (PDF) Checked 2026-09-27.
- Ideal Heating (Ideal group), Logic Combi2 C24, C30, C35: Logic Combi2 user guide, UIN 237664 A01 (10/2023) (PDF) Checked 2026-09-27.
- Ideal Heating (Ideal group), Logic Max Combi2 C24, C30, C35: Logic Max Combi2 user guide, UIN 228290 A06 (October 2022) (PDF) Checked 2026-09-27.
- Ideal Heating (Ideal group), Logic Combi C24, C30, C35 (first generation): User guide Logic Combi C 24 30 35 (PDF) Checked 2026-09-27.
- Viessmann (Viessmann group), Vitodens 100-W/111-W/111-F/141-F (black/white screen): Operating instructions for the system user, 6167584 GB (12/2020) (PDF) Checked 2026-09-27.
- Danfoss (Danfoss group), RAS-C thermostatic sensor (013G5015, 013G5016): Data sheet Thermostatic sensor RAS-C, VDFNQ302 (05/2015) (PDF) Checked 2026-09-27.
- Danfoss (Danfoss group), RAS-C² thermostatic sensor (013G6040): Data sheet Thermostatic sensor RAS-C² with RA-N presetting valve, AI087886402550en-010402 (12/2025) (PDF) Checked 2026-09-27.
- Honeywell Home (Resideo) (Resideo / Honeywell Home group), VT15 / VTL15 thermostatic radiator valve: VT15, VTL15 radiator valves product specification sheet, EN0H-2041GE23 R0121 (PDF) Checked 2026-09-27.
- IMI Heimeier (IMI Heimeier group), Thermostatic head K: Thermostatic head K data sheet, EN ed.3 10.2017 (PDF) Checked 2026-09-27.
- Drayton (Drayton group), TRV4 thermostatic radiator valve: TRV4 thermostatic radiator valve information sheet (PDF) Checked 2026-09-27.