Older 100-W boilers have a pressure gauge, a small screen, then two round knobs. If yours is a black screen with buttons and no knobs, use the 050-W steps instead.
- The right rotary selector with the radiator symbol sets the heating flow. Leave the tap knob if you only came to lower the heating.
- Turn it towards 0 to lower the flow, or towards 6 to raise it. Keep it high enough that rooms can still reach temperature if you have a room thermostat.
- Stop around 55°C if the house still warms. Add time on the programmer if rooms take longer to come up.
Look up your exact model on Boiler Manuals if the fascia does not match. If the fascia is a black screen with no knobs, go to the Vitodens 050-W steps. Then return to the Viessmann flow-temperature page or the Boiler Optimiser.