Heater will not start; display shows E01 shortly after power-up.

Safety first: Switch off the heater at the isolator and turn off the pool pump before touching any pipework. Do not run the heater without adequate water flow.

• Check filtration system: Clean the pool skimmer basket and pump strainer basket. Backwash or clean the filter to restore normal flow.
• Verify valves: Ensure all inlet and outlet valves to the Elecro heater are fully open. Check for any bypass valves that may be diverting flow away from the heater.
• Bleed air: If the system was recently drained or serviced, bleed air from high points in the pipework or filter to remove air locks that can reduce flow.
• Inspect flow switch: Locate the Elecro in-line flow switch on the heater’s water manifold. Check for debris or scale around the paddle or turbine (depending on model). Clean gently and ensure it moves freely.
• Electrical check (advanced): With power isolated, inspect the flow switch wiring harness to the control PCB for loose or damaged connectors. Re-seat plugs firmly.

If E01 persists after restoring good flow and cleaning the switch, the flow switch assembly may need replacement.