Thermostat shows error 105 and cannot control domestic hot water temperature from the app or screen.

Safety: Isolate boiler power before touching any internal wiring. Only access user panels if allowed by the manual.

• Check configuration: In the thermostat installer menu, confirm that DHW control is enabled and that the system type (combi/system boiler with cylinder) is correctly selected.
• Verify boiler support: Consult the boiler manual to ensure it supports remote DHW setpoint control via bus. Some models only allow DHW control from the boiler panel.
• Inspect DHW sensor connection: At the boiler, visually check the domestic hot water NTC sensor plug and wiring for disconnection or damage (do not open sealed combustion areas).
• Test DHW temperature: Run hot water and see if the boiler modulates correctly when using its own controls. If DHW is unstable or cold, the DHW NTC sensor may be faulty and should be replaced by a technician.