Furnace displays E08 and shuts down; may be accompanied by rapid temperature rise on the display.

Safety: Turn off power and allow the Viadrus furnace to cool. Do not attempt to open any part of the water circuit while hot.

• Verify pump operation: With power restored, call for heat and touch the circulation pump body carefully. It should vibrate and get warm. If silent and cold, check the electrical connection and fuse. If humming but not turning, free the shaft as per pump manufacturer instructions.
• Check valves: Confirm that the service valves on the flow and return connections at the furnace are fully open. Partially closed valves can cause overheating.
• Clean heat exchanger: On older Viadrus cast‑iron section furnaces, internal waterways can sludge up. A heating professional can isolate the furnace and flush the heat exchanger using a chemical cleaner compatible with cast iron.
• Adjust pump speed: If the pump has multiple speed settings, ensure it is not set to the lowest speed on a large system. Increase speed one step and monitor operation.
• Reset and test: After resolving circulation issues, reset the control and monitor the temperature rise. If E08 recurs, further hydraulic analysis by a technician is recommended.