Boiler displays E20; may indicate safety chain open (e.g., overheat, door, or other safety device open).

Safety first: Do not bypass safety devices. Isolate power and allow the boiler to cool.

• Identify safety devices: Refer to the wiring diagram to locate all safety thermostats and cut-outs in series with the control circuit.
• Check for manual reset: Some safety thermostats have a reset button. Once the boiler is cool, press the reset until it clicks.
• Inspect wiring: Check continuity through the safety chain using a multimeter. Look for loose spade connectors or broken wires.
• Investigate cause of trip: If a safety device has tripped, determine why (e.g., pump failure, blocked heat exchanger) before resetting.
• Replace faulty device: Any thermostat or cut-out that will not reset or has poor continuity must be replaced with the correct Elnur part.