Heater display shows erratic or jumping temperature readings while water temperature is stable.

Safety first: Turn off power before handling sensor wiring.

Step-by-step checks:

• Reseat connectors: Unplug and replug the temperature sensor connectors at the control board to ensure good contact.
• Inspect cable routing: Ensure the sensor cable is not bundled tightly with pump or blower power cables. If it is, reroute it away from high-voltage lines.
• Check for moisture: If the sensor terminates in a junction box, open it and look for condensation. Dry thoroughly and reseal.
• Replace sensor: If readings remain erratic, replace the Pahlen sensor with a new OEM part.

When to stop: If a new sensor and proper routing do not stabilize readings, the control board input may be faulty.