How to Fix / Troubleshooting

Safety: Turn off power and let the boiler cool before removing any sensor.

Locate the boiler temperature sensor inserted into the boiler pocket (usually on the front or side of the heat exchanger).
Check that the sensor is fully inserted and clamped; a partially inserted sensor can read incorrectly.
Inspect the cable for damage and ensure the connector is firmly seated on the control board.
Bleed air from the boiler and nearby piping to ensure water is in contact with the sensor pocket.
If available, measure sensor resistance and compare with Defro specifications. Replace if out of range.

If the sensor tests good but E06 persists, the control board input may be faulty and requires professional diagnosis.

E06 displayed; furnace does not respond to temperature changes or shows unrealistic boiler temperature

Possible Causes