Heater will not start; display shows H1 shortly after a call for heat.

Safety first: Turn off power to the heater at the breaker and stop the circulation pump before opening any equipment. Do not run the heater without proper water flow; heat exchanger damage and fire risk are possible.

• Check pump and skimmer baskets: Remove leaves and debris from the pump strainer basket and skimmer baskets. Restore flow and restart the system.
• Backwash or clean the filter: If you have a sand filter, backwash until the sight glass runs clear. For cartridge filters, remove cartridges and hose them thoroughly from top to bottom. Reassemble and restart.
• Verify valves: Ensure all AstralPool multiport and isolation valves on the heater inlet and outlet are fully open and that any bypass valve is not diverting too much water away from the heater.
• Inspect the flow/pressure switch: Locate the AstralPool flow switch or pressure switch on the heater water manifold. Check for loose wiring and corrosion on terminals. With the pump running, the switch should close; if it remains open, it may be faulty and require replacement.
• Bleed air from system: If the system was recently opened, bleed trapped air from the filter’s air relief valve until a solid stream of water appears.

If H1 persists after restoring proper flow and cleaning the filter, have a technician test the flow switch and water pressure at the heater inlet.