Boiler shows E08, will not start, sometimes accompanied by loud humming from pump area.

Safety: Isolate power and allow the boiler to cool. Some water spillage may occur when working on the pump.

• Check system pressure: Ensure the pressure gauge reads at least 1.0 bar. Low pressure can cause pump cavitation and E08.
• Bleed air: Bleed air from the pump (if it has a bleed screw) and from radiators. Re-pressurise the system as needed.
• Manual freeing (engineer level): Remove the pump front screw (if fitted) and gently turn the pump shaft with a screwdriver to free it. Replace the screw and test.
• Clean system filter: If a Thermona system filter or strainer is installed on the return, isolate and clean it to restore flow.
• Electrical test (engineer level): Check voltage at the pump terminals when there is a heat demand. If voltage is present but the pump does not run, replace the pump head or complete pump assembly.