Safety first: Turn off power to the heater before adjusting wiring.

Step-by-step checks:

Verify control mode: On the Pahlen user interface, confirm whether the heater is set to internal thermostat mode or external control (e.g., pool automation). Set it according to your installation.
Inspect external control wiring: Open the control compartment and locate the low-voltage terminals for external thermostat/automation. Check that wires are firmly attached and not shorted together or to ground.
Bypass test (if allowed): If the heater is supposed to be controlled externally, temporarily disconnect the external wires and configure the heater to internal control. Set a temperature above current water temperature and see if the heater starts. If it does, the issue is with the external control system.
Check external sensor (if installed): If a Pahlen remote water sensor is used, test its resistance and compare to the temperature chart. Replace if out of range.

When to stop: If you are unsure about low-voltage wiring or automation integration, consult a pool professional or Pahlen service technician.

Heater displays E10 and will not fire; often associated with external control or thermostat issues.

Possible Causes