Boiler displays A15, no response to thermostat demand, heating symbol may flash

Safety: Isolate power before touching any control wiring. Low-voltage circuits can still be damaged by short circuits.

User checks:

• Thermostat settings: Ensure the room thermostat or Fondital remote control is set to heating mode and a temperature above room temperature.
• Batteries: Replace batteries in wireless thermostats or remote controls.
• Manual mode: If available, set the boiler to manual or test mode to see if it can heat independently of the thermostat.

Technician actions:

• Check continuity of the room thermostat wiring to the boiler terminals.
• Verify correct configuration of the Fondital control board jumpers for external controls.
• Test the room thermostat / chronothermostat and replace if defective.
• Check the main PCB input circuit for the thermostat.