Furnace shows E11 and remains locked out; no response to thermostat, often after a power surge or wiring work.

Safety: Isolate power before removing the control panel cover.

• Power reset: Turn off the furnace at the main switch or breaker for at least 5 minutes, then restore power. Sometimes this clears transient memory errors.
• Inspect connectors: Remove the control board cover and carefully check all multi‑pin connectors for full insertion. Gently press each connector into place.
• Check supply voltage: Measure mains voltage at the furnace terminals. Ensure it is within the range specified on the Viadrus rating plate. Install surge protection if voltage is unstable.
• Board replacement: If E11 persists, the main control board is likely defective. Replacement should be carried out by an authorized Viadrus service technician to ensure correct configuration and safety checks.