Thermostat display is completely blank and does not respond to button presses.

Danger: Power circuits may be at mains voltage. Always isolate at the main breaker and verify with a tester before touching any wires.

• Step 1 – Check breaker and switches:
  • Verify that the boiler/thermostat circuit breaker is ON.
  • Check any local isolation switches near the boiler.
• Step 2 – Inspect thermostat connection:
  • Remove the thermostat from its wall plate.
  • Ensure it is correctly seated and that connector pins are not bent.
• Step 3 – Measure supply voltage:
  • Use a multimeter to check for the correct voltage at the thermostat power terminals or wall plate.
  • If no voltage is present, trace back to the boiler or power supply.
• Step 4 – Check boiler transformer (if applicable):
  • On 24V systems, verify that the boiler’s low-voltage transformer is outputting the correct voltage.
• Step 5 – Replace thermostat if power is present but display is dead:
  • If correct voltage is present at the thermostat but it remains blank, the internal electronics are likely failed.
  • Replace the Protherm smart thermostat.