Heater's internal circulation (on models with built-in pump) is noisy or fails to move water.

Safety first: Turn off power and close isolation valves before servicing the internal pump. Allow hot water to cool.

Step-by-step checks:

• Bleed air: Open any bleed screw on the pump housing to release trapped air, then close it once water flows steadily.
• Check for debris: Remove the pump strainer cover (if present) and clean out debris. Inspect the impeller for blockage.
• Spin shaft: With power off, try to rotate the pump shaft manually (using the access at the rear if provided). If it is stuck, the motor may be seized.
• Electrical test: A technician can test the pump windings and capacitor to determine if replacement is needed.

When to stop: Internal pump replacement should be done by a technician familiar with Pahlen heaters to ensure proper sealing and wiring.