Unit displays error code 20 and will not operate; may occur after power issues or internal fault.

Safety first: Turn OFF power and gas. Do not attempt to bypass any safety devices.

Steps to check and correct:

• Inspect wiring to hi-limit: Remove the front cover and locate the hi-limit switch and associated wiring harness. Check for loose connectors, burnt insulation, or broken wires. Reseat connectors firmly.
• Check for signs of overheating: Look for discoloration or scorching on the heat exchanger, wiring, or plastic parts. If present, the unit may have experienced severe overheating and should be inspected by a professional.
• Power reset: Turn off power at the breaker for 5 minutes, then restore. Sometimes a control lockout can be cleared if the underlying cause has been resolved.
• Professional diagnosis: If error 20 returns immediately, the PCB or hi-limit assembly is likely defective. These components should be tested and replaced by a Noritz-authorized technician using OEM parts.