Boiler display shows E0 and burner will not start

Safety first: Turn off power to the boiler at the service switch and shut off gas if you will be opening the burner compartment. Use a multimeter only if you are comfortable and qualified.

• Check thermostat settings: Verify the room thermostat is set to HEAT and the setpoint is above room temperature. Replace batteries if it is a battery-powered thermostat.
• Inspect thermostat wiring: Remove the boiler front panel and locate the low-voltage thermostat terminals (often marked T-T or R-W on Pennco controls). Confirm wires are firmly attached and not corroded or broken.
• Bypass test: With power OFF, temporarily jumper the thermostat terminals at the boiler (T-T). Restore power and see if the E0 clears and the boiler starts. Remove jumper after test.
• If boiler runs with jumper: The issue is likely the thermostat or thermostat cable. Replace the thermostat or repair/replace the low-voltage cable.
• If E0 remains with jumper: The fault may be in the integrated boiler control board. Inspect for burnt traces or water damage. If present, the control board should be replaced by a qualified technician.