Boiler control display shows E0 and burner will not start

Safety first: Turn off power to the boiler at the service switch and shut off the gas valve before removing any covers. Allow the boiler to cool.

Steps to try:

• Power reset: Turn off the boiler power for 2–3 minutes, then restore power and see if the E0 clears.
• Check low-voltage wiring: Remove the front panel and inspect the wiring harness to the Peerless control module (e.g., Peerless MCBA or PSC control). Look for loose plugs, pinched wires, or corrosion on the terminal strip.
• Verify thermostat/TT circuit: Confirm the thermostat or external control is wired correctly to the TT terminals and not shorted. Disconnect TT and jumper the terminals briefly to see if the code changes.
• Check sensor connections: Ensure the supply and return temperature sensors and flue sensor are firmly plugged into the control board and not damaged.
• If E0 persists: The control may be locked out due to an internal fault. Do not bypass safeties. Contact a qualified technician to test the control module and replace it if necessary.