Use the arrow buttons to reach your desired heat. For safety, the system typically won't allow temperature changes while water is actually flowing at high temperatures.
If the heater is left in standby for more than 10 minutes, priority is often released, and high temperatures (above 50°C) may reset to a safer 48°C for the next user. tgc bc-90-1h manual
Press the [On/Off] button. The display should light up, showing the previously saved temperature (often defaulting to 42°C for new installations). Use the arrow buttons to reach your desired heat
Simply turn on your shower or faucet. The heater will ignite automatically. Safety and Maintenance priority is often released