Summer mode (hot water only) and winter mode (heating and hot water)
Summer mode switches central heating off and leaves hot water on; winter mode has both on.
What the manual says to do
Worcester Bosch Greenstar 2000: press the radiator key and keep pressing the arrow key until the summer symbol appears. Vaillant: set the heating flow temperature to ‘Heating off’. Ideal Logic Combi2: press Mode until a cross is through the radiator but not the tap (summer), or through neither (winter). Go back to winter mode before cold weather.
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
Summer mode does not switch the boiler off: hot water, and on most boilers the heating controls and timer, stay live. It is not the clock’s summer-time change, which Viessmann’s manual calls the wintertime/summertime changeover.
- What it looks like
- Summer: the radiator crossed out or dropped, with the tap still shown. Winter: the tap and the radiator together. Ideal’s first Logic Combi had a mode knob with a tap position (summer) and a tap-and-radiator position (winter).
- Names used
- Summer mode (Worcester Bosch, Vaillant); Summer and Winter Conditions (Ideal); Heating off, hot water on
Where makers differ
Frost protection is where makers differ most: Worcester Bosch says “Frost protection is not available in summer mode” and to leave summer mode if frost is likely, while Ideal’s frost protection operates in all modes and Ideal asks for winter mode when a system frost thermostat is fitted.
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 (Worcester Bosch, Vaillant, Ideal Heating, Viessmann), each fetched and read on the date shown:
- Worcester Bosch, Greenstar 2000 combi (GR2301iW): Greenstar 2000 user instructions, 6 721 839 343 (2023/04) UK/IE (PDF) — “The heating pump and consequently the heating are switched off in summer mode. The DHW supply and also the power supply for heating controls and timer remain active … Frost protection is not available in summer mode.” 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) — “Switching off heating mode (Summer mode) … set the heating flow temperature to Heating off”; displayed symbol “Summer mode active — Heating mode is switched off”. Checked 2026-09-27.
- Ideal Heating, Logic Combi2 C24, C30, C35: Logic Combi2 user guide, UIN 237664 A01 (10/2023) (PDF) — “Summer Conditions (Domestic Hot Water only required): Press the mode button until a cross is shown through the radiator, but a cross is not shown through the tap”; winter conditions: no cross through the radiator; the boiler must be in winter mode for a system frost thermostat to run. Checked 2026-09-27.
- Ideal Heating, Logic Combi C24, C30, C35 (first generation): User guide Logic Combi C 24 30 35 (PDF) — Mode knob (C) with a ‘winter’ position drawn as a tap and radiator and a ‘summer’ position drawn as a tap; “Summer Conditions — (Domestic Hot Water only required)”. 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) — “Wintertime/summertime changeover — This changeover is automatic” (the clock, not a heating mode). Checked 2026-09-27.
Written in our own words; quotations are the makers’ wording.