Fondital Short Cycling / Oversized Boiler or Sensor Misreading

Boiler runs for only a short time then stops, radiators never reach set temperature

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Possible Causes

Flow temperature set too high on Fondital boiler, Incorrect NTC sensor readings, Poor system volume or missing bypass, Pump over-speed causing rapid temperature rise

How to Fix / Troubleshooting

Safety: No immediate hazard, but efficiency is reduced.

User checks:

  • Lower flow temperature: Reduce the heating flow temperature setting to around 60°C and observe if run times increase.
  • Open more radiators: Ensure enough radiators are open to absorb boiler output.

Technician actions:

  • Check flow and return NTC sensors for accuracy.
  • Verify correct pump speed and adjust if necessary.
  • Install or adjust an automatic bypass valve if required.
  • Review system design vs. boiler output and adjust settings (e.g., maximum power) on the Fondital PCB.
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Repair Difficulty

Easy 2/5

Required Part

Automatic Bypass Valve
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