Safety: Turn off boiler power at the main switch before opening any covers. Low-voltage circuits are still powered from mains equipment.

Step 1 – Check boiler power: Confirm the boiler itself is powered and its display is on.
Step 2 – Inspect thermostat wiring: Remove the thermostat from the wall plate and verify that the power terminals (e.g., +/– or 24 V) have firmly connected wires.
Step 3 – Measure voltage: With a multimeter and appropriate skills, measure the voltage at the thermostat power terminals. If no voltage is present, trace back to the boiler or transformer.
Step 4 – Check boiler fuse: On the Immergas boiler control board, locate the low-voltage fuse feeding the thermostat circuit. Replace only with the same type and rating if blown.
Step 5 – Replace transformer: If an external 24 V transformer is used and no output is measured, replace it with a compatible unit.
Step 6 – Replace thermostat: If correct voltage is present at the thermostat but the screen remains blank, the thermostat is defective and must be replaced.

Thermostat screen completely blank, no lights or response

Possible Causes