Pentair Pool Heater ERR HLS Error Code

Updated 2026-08-29 · review status: manual-verified Last verified: 2026-08-29

Quick answer

High Limit Switch Water temperature at or near the heat exchanger outlet reached an unsafe level. The high limit switch opened to protect the equipment. Low water flow through the heat exchanger (bypass too wide open, low pump speed, dirty filter), scaled heat exchanger reducing flow and concentrating heat, failed or degraded HLS switch. Allow 15 minutes for cooling. Press the manual HLS reset but

Severity: high · DIY difficulty: intermediate

Safety

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What ERR HLS means

High Limit Switch Water temperature at or near the heat exchanger outlet reached an unsafe level. The high limit switch opened to protect the equipment. Low water flow through the heat exchanger (bypass too wide open, low pump speed, dirty filter), scaled heat exchanger reducing flow and concentrating heat, failed or degraded HLS switch. Allow 15 minutes for cooling. Press the manual HLS reset button inside the heater cabinet. Verify pump speed and bypass valve position before restarting. If ERR HLS trips repeatedly, inspect the heat exchanger for calcium scale and confirm adequate flow rate.

Causes, ranked

  1. 1. Low water flow through the heat exchanger (service pump and filter) common diy-ok

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    Fix:

  2. 2. Inlet water temperature above 104°F occasional diy-ok

    Check:

    Fix:

  3. 3. Failed high limit switch (HLS) occasional pro-only

    Check:

    Fix:

Parts & supplies for Pentair Pool Heater: filters, control boards, sensors, and common replacement parts.

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Sources

  • PoolDial error-code reference (manual-backed) — verified 2026-08-29
  • Pentair MasterTemp/Max-E-Therm Heater Installation & User's Guide (Section 5 Troubleshooting) — verified 2026-08-29