Boiler displays E07 and will not fire even though system pressure is normal

Safety: Turn off power and allow the boiler to cool before opening any water connections.

• Bleed air: Air trapped in the boiler or near the flow sensor can prevent proper operation. Bleed air from high points in the system and from the boiler's built-in air vent if present.
• Check circulator operation: Confirm the Dettson primary circulator pump is running during a call for heat. If not, the flow sensor may not detect movement. A technician may need to replace the pump or relay.
• Inspect flow switch/sensor: Locate the Dettson flow switch or turbine sensor on the boiler's water path. Check for loose wiring and secure connectors. Some models have a removable strainer that can be cleaned of debris.
• Reset and test: After clearing air and cleaning strainers, reset the boiler and observe if E07 clears. If the code returns, the flow switch/sensor itself may be defective and should be replaced.