Pool heater will not start; display shows E01 shortly after power-up

Safety first: Turn off power to the BWT pool heater at the breaker and stop the circulation pump before opening any plumbing connections.

Step-by-step checks:

• Verify valves fully open: Confirm the pool return, suction, and heater bypass valves are fully open to allow proper flow through the heater.
• Clean skimmer and pump baskets: Remove debris from the skimmer basket and pump strainer basket to restore flow.
• Check and clean inlet filter/strainer: If your BWT heater has an integrated inlet strainer, remove the cover, pull out the screen, and rinse it thoroughly with a hose.
• Inspect filter pressure: If the pool filter pressure is high, backwash or clean the filter to improve flow.
• Check BWT flow switch/flow sensor: Locate the flow switch or flow sensor on the heater’s water inlet line. Inspect wiring for damage or loose connectors. If the paddle or turbine is jammed with debris, carefully clean it. If the switch does not click or the sensor is seized, replacement may be required.
• Restart system: Restore power, start the circulation pump, bleed air from the system if needed, and then restart the heater to see if E01 clears.

If E01 persists after restoring proper flow and cleaning components, the flow switch/flow sensor may be defective and should be replaced or tested by a qualified technician.