Viadrus Condensation Corrosion / Low Return Temperature Damage

Corrosion and rust visible on the lower sections of the Viadrus cast‑iron furnace, with occasional water drops.

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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

Prolonged operation with low return water temperature, Missing or misadjusted mixing valve, Oversized furnace running at low load, Poor flue draft causing condensation

How to Fix / Troubleshooting

Safety: Turn off power and allow the furnace to cool before inspection.

  • Check return temperature: Use the control display or a thermometer to ensure return water temperature stays above the minimum recommended by Viadrus (often around 55°C for cast iron).
  • Install/adjust mixing valve: If not present, have a 3‑way or 4‑way mixing valve installed for return temperature protection. If present, adjust to maintain higher return temperature.
  • Improve load matching: Avoid running the furnace at very low load for long periods. A technician may recommend a buffer tank.
  • Assess damage: If sections are heavily corroded or leaking, replacement of affected cast‑iron sections or the entire furnace may be necessary.
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Repair Difficulty

Professional Required 5/5

Required Part

Cast‑Iron Heat Exchanger Sections
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