Display shows HTR or HEATER FAIL; water does not heat even though pumps run.

Safety: Always shut off power at the GFCI before accessing the heater or control pack. Heater terminals carry lethal voltage.

• Check for other codes: Look for accompanying OH, HL, Sn1, or Sn2 codes that may indicate sensor or overheat issues rather than a bad heater.
• Inspect heater connections: With power OFF, remove the equipment bay panel and verify that the heater wires are firmly attached and not burned or discolored.
• Test heater element: Disconnect both heater leads and measure resistance across the heater terminals. An infinite reading indicates an open element; near 0 ohms indicates a short. Either condition requires heater replacement.
• Check for external reset: Some Hydropool heaters have a manual reset button on the heater housing. If present, press it firmly until it clicks, then restore power and test.
• Control board diagnosis: If the heater tests good but does not receive power when there is a heat demand, the control board or relay is likely faulty and should be tested and replaced by a technician.