Heater starts and stops frequently with short cycles; water temperature overshoots or undershoots setpoint.

Safety first: Turn off power before adjusting sensors or opening panels.

Step-by-step checks:

• Verify sensor location: Ensure the Pahlen water temperature sensor is installed in a well-mixed location (e.g., heater outlet or dedicated sensor well) and not in a dead-end or stagnant area.
• Check flow rate: Confirm that the pump and valves provide adequate flow through the heater. Very low flow can cause rapid outlet temperature rise and short cycling.
• Compare temperatures: Use an accurate pool thermometer to compare actual water temperature with the heater's displayed value. A large discrepancy suggests a sensor or calibration issue.
• Adjust setpoint and differential (if available): Some Pahlen controllers allow adjustment of temperature differential or hysteresis. Increasing the differential can reduce short cycling.

When to stop: If the heater is significantly oversized or sensor calibration is off, consult a technician for possible controller reconfiguration or system redesign.