Pentair Pool Heater ERR AFS Error Code
Quick answer
Air Flow Switch Combustion air flow problem detected during the pre-purge cycle. The blower vacuum switch did not detect the expected negative pressure, so the ignition sequence was aborted. Blocked vent termination (bird nests, leaves, ice), weakening blower motor, cracked or disconnected vacuum tubing on the AFS switch, failed AFS switch, vent configuration exceeds maximum length/bends. Inspect
Severity: high · DIY difficulty: intermediate
Safety
TBD - must be written per-code before publish
What ERR AFS means
Air Flow Switch Combustion air flow problem detected during the pre-purge cycle. The blower vacuum switch did not detect the expected negative pressure, so the ignition sequence was aborted. Blocked vent termination (bird nests, leaves, ice), weakening blower motor, cracked or disconnected vacuum tubing on the AFS switch, failed AFS switch, vent configuration exceeds maximum length/bends. Inspect the exhaust vent termination for blockages. Listen for the blower — it should run for ~30 seconds before ignition. Check the rubber tube connecting the blower housing to the AFS for cracks or kinks. If the blower is weak or noisy, the motor capacitor may need replacement.
Causes, ranked
1. Blockage in blower intake, heat exchanger, or exhaust (or over-long indoor vent run) common diy-ok
Check:
Fix:
2. Air flow switch tubing misrouted, kinked, disconnected, or punctured common diy-ok
Check:
Fix:
3. Failed air flow switch (AFS) occasional pro-only
Check:
Fix:
4. Failed blower occasional pro-only
Check:
Fix:
Parts & supplies for Pentair Pool Heater: filters, control boards, sensors, and common replacement parts.
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