Hayward Pool Heater AO / AC Error Code
Quick answer
Blower Vacuum Switch Error AO means vacuum switch won't close (no air movement detected). AC means vacuum switch won't open (stuck closed). Blower not running or running weakly, vacuum switch tubing blocked/cracked/disconnected, vent restriction or improper venting configuration, failed vacuum switch. Check that blower motor spins freely and runs when called. Inspect vacuum switch tubing for crack
Severity: high · DIY difficulty: intermediate
Safety
TBD - must be written per-code before publish
What AO / AC means
Blower Vacuum Switch Error AO means vacuum switch won't close (no air movement detected). AC means vacuum switch won't open (stuck closed). Blower not running or running weakly, vacuum switch tubing blocked/cracked/disconnected, vent restriction or improper venting configuration, failed vacuum switch. Check that blower motor spins freely and runs when called. Inspect vacuum switch tubing for cracks, kinks, or blockages. Verify vent termination is clear of debris or bird nests. Test vacuum switch with manometer if available.
Causes, ranked
1. AO: blower prover (vacuum) switch does not close after blower start - blocked blower intake or exhaust common diy-ok
Check:
Fix:
2. AO: failed blower prover switch or weak blower occasional pro-only
Check:
Fix:
3. AC: prover switch closed before blower start-up (stuck closed) occasional pro-only
Check:
Fix:
Parts & supplies for Hayward Pool Heater: filters, control boards, sensors, and common replacement parts.
Sources
- PoolDial error-code reference (manual-backed) — verified 2026-08-29
- Hayward H-Series H150FD-H500FD Service & Installation Manual (Figure 27: Error codes) — verified 2026-08-29
- PoolDial error-code reference (manual-backed) — verified 2026-08-29