Furnace locks out with E04, often after running for a short period, casing may feel very hot.

Safety: Turn off power and allow the furnace to cool completely before touching any panels. Overheating can damage components and pose a fire risk.

User checks:

• Ensure all supply and return vents in the property are open and not blocked by furniture or rugs.
• Check that the furnace filter (if fitted in the air handling system) is clean and not clogged.
• After cooling, reset the furnace according to the Ravenheat manual and observe if E04 reoccurs.

Technician checks:

• Test the overheat thermostat for correct operation and continuity when cool.
• Inspect the primary heat exchanger for heavy scale, soot, or blockage and clean as per manufacturer instructions.
• Verify correct operation of the circulation pump or blower fan and check for seized bearings or failed capacitors.
• Confirm correct system flow rates and that any zone valves or balancing valves are not stuck closed.

Repeated E04 trips indicate a serious underlying issue; continued operation can damage the heat exchanger.