Boiler shows F.06, will not fire, sometimes after power surge or wiring work

Safety first: Turn off power and allow the boiler to cool. Close isolation valves if you will open any water components.

• Verify system valves: Confirm all service valves around the boiler, closely spaced tees, and primary loop are fully open.
• Check system pressure: Ensure the system is properly filled and pressurized. Low pressure can reduce flow and prevent the flow switch from closing.
• Inspect circulator operation: During a call for heat, the primary circulator should run. If it does not, check the pump's power connection and any external pump relay. A seized pump or failed motor will need replacement.
• Clean or exercise flow switch: Locate the flow switch on the boiler piping (often a paddle or turbine type). Remove the switch per the manual. Inspect for debris, scale, or sludge preventing movement. Clean gently and reinstall with correct orientation and arrow direction.
• Flush heat exchanger: If the boiler is older or on hard water, internal restriction may be present. A professional should perform a chemical flush of the Lochinvar heat exchanger using approved descaling solution.

Professional help: If F.06 persists after verifying flow and cleaning the switch, the flow switch or control board input may require replacement by a technician.