Interrupted or shorted return (inlet) thermistor.
- Check the electrical connection to the appropriate thermistor. Verify 5 VDC by checking in Molex connector. If not 5 VDC, check harness. If harness is OK, replace control. NOTE: Boiler will reset automatically. Verify thermistor values by referencing chart in this manual.
- If connection is okay, replace thermistor.
