E12
Viadrus
Return Temperature Too Low / Condensation Protection
Display shows E12, burner stops, and the circulation pump may continue to run.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Undersized bypass or mixing valve on Viadrus cast‑iron boiler, Excessive flow of cold return water, Faulty return temperature sensor, Incorrect system hydraulics
How to Fix / Troubleshooting
Safety: Turn off power before adjusting any internal wiring. Hydraulic adjustments should be done with the system cool when possible.
- Check mixing valve: If your Viadrus cast‑iron furnace is installed with a 3‑way or 4‑way mixing valve for return temperature protection, verify that it is not stuck in a position that allows very cold water to return. Exercise the valve through its full range.
- Bypass line: Ensure the bypass line between flow and return (if fitted) is open and not blocked. This helps maintain minimum return temperature.
- Sensor check: Test the return NTC sensor as described for E06. Replace if faulty.
- System balancing: A heating engineer may need to rebalance the system or adjust pump speed to prevent excessive cooling of the return water, which can damage a Viadrus cast‑iron heat exchanger over time.
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Repair Difficulty
Hard
4/5
Required Part
Return Temperature Protection Mixing Valve
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