Boiler display shows E0 and unit will not fire

Safety first: Turn off power to the boiler at the breaker and close the gas shutoff valve before removing any covers. Only work inside the control compartment if you are comfortable and qualified to do so.

• Step 1 – Power reset: Turn off the boiler at the breaker for 5 minutes, then restore power. Check if E0 clears. If it returns immediately, continue.
• Step 2 – Inspect line power: Verify correct voltage (typically 120 VAC in North America) and proper polarity at the boiler’s power terminals using a multimeter. Correct any wiring issues at the junction box or disconnect.
• Step 3 – Check harness connections: Remove the front panel. Locate the wiring harness between the user interface (front display) and the main control PCB. Unplug and firmly reseat all connectors, checking for bent pins, corrosion, or damaged insulation.
• Step 4 – Inspect for moisture or heat damage: Look for signs of water ingress, burnt spots, or discoloration on the display board and main PCB. If present, the affected board must be replaced.
• Step 5 – Replace suspect board: If wiring is intact and voltage is correct but E0 persists, replace the user interface PCB first (most common). If the fault remains, replace the main control PCB. Follow the service manual for correct part numbers and configuration.

Warning: Incorrect wiring or PCB replacement can cause further damage or unsafe operation. If you are not experienced with boiler electronics, contact a qualified Rheem service technician.