Code 20, furnace unresponsive to thermostat, no call for heat recognized

Safety: Turn off power before accessing the wiring terminals.

• Check thermostat settings: Ensure the room thermostat or programmer is set to HEAT and the setpoint is above room temperature.
• Inspect wiring: At the furnace control terminal strip, verify that the thermostat connections are secure and not corroded. Tighten loose screws.
• Bypass test (qualified persons only): With power OFF, temporarily link the thermostat terminals at the furnace. Restore power; if the furnace now responds, the external thermostat or its wiring is faulty.
• Replace faulty control: Fit a compatible Vokera-approved room thermostat or repair wiring as needed.