Tap: hot water
The hot-water side of the boiler: on a combi, the water heated for your taps and shower as you use it; on a system boiler, the hot-water cylinder. When it is lit, hot-water mode is on; Vaillant and Worcester Bosch make it flash or add the burner symbol while tap water is being heated.
What the manual says to do
Press the tap key or turn the tap knob to set the hot-water temperature. Ideal limits it to about 40–65 °C and notes that at low flow rates it may exceed 65 °C. Worcester Bosch warns that if the heating side is set above 65 °C, water at the tap can briefly run hotter than the set point after the boiler switches over, and advises a thermostatic mixing valve at the bath or shower to protect vulnerable people from scalding.
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.
What it does not mean
On a combi it does not mean hot water is stored and waiting: the water is heated when you open a tap, unless pre-heat or comfort mode is on. It is not a legionella setting.
- What it looks like
- A tap with a drop or a stream of water, sometimes with wavy lines for heat. Steady, flashing or crossed through, on a key, a knob or the display.
- Names used
- Domestic hot water, DHW (Worcester Bosch); Hot water generation active (Vaillant); Hot water request (Baxi); Domestic Hot Water (Ideal); DHW heating (Viessmann)
Where makers differ
Worcester Bosch Greenstar 2000: the tap flashes in hot-water mode and the burner symbol appears when it fires. Vaillant: steady means draw-off mode before the burner is on, flashing means the burner is on in draw-off mode. Ideal Logic Max shows ‘Ready’ or ‘On’ under the tap; Baxi lists it as ‘Hot water request’.
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, Worcester Bosch, Baxi, Ideal Heating), 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) — Displayed symbols: “Hot water generation active — Permanently on: Draw-off mode before burner is on; Flashing: Burner on in draw-off mode”. Checked 2026-09-27.
- Worcester Bosch, Greenstar 2000 combi (GR2301iW): Greenstar 2000 user instructions, 6 721 839 343 (2023/04) UK/IE (PDF) — “Hot water mode On / Hot water mode Off”; “The * symbol flashes in the display in DHW mode. The B symbol also appears if the burner is active”; scalding warning and advice to fit a thermostatic mixing valve (TMV) if the CH temperature is changed to above 65 °C. 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: “Hot water request”; “Hot water temperature control (Combi only)”. Checked 2026-09-27.
- Ideal Heating, Logic Max Combi2 C24, C30, C35: Logic Max Combi2 user guide, UIN 228290 A06 (October 2022) (PDF) — “The domestic hot water temperature is limited by the boiler controls to a maximum temperature of 65ºC … At low DHW draw off rates the maximum temperature may exceed 65ºC”; hot water temperature (approx.) minimum 40 ºC, maximum 65 ºC; ‘Ready’ or ‘On’ shown under the Tap symbol. Checked 2026-09-27.
Written in our own words; quotations are the makers’ wording.