5 flashes = Vacuum switch / draft fault. The unit can\'t establish proper venting and locks out for safety. Same diagnostic as State and AO Smith family 5-flash codes.
What\'s happening
On atmospheric Reliance gas heaters, the vacuum switch confirms adequate draft through the chimney before allowing the burner to fire. On Power Vent (6-PVRT), the switch confirms the fan is running and producing exhaust pressure. Either condition not met → 5 flashes.
Atmospheric (6-NORT / 9-NORT / 12-NORT) — diagnostic sequence
1. Inspect the chimney for obstruction
- Bird nests at the chimney cap (most common after spring)
- Snow or ice blocking the cap
- Collapsed B-vent connector or rust holes
- Disconnected vent connector at the draft diverter
2. Back-drafting check
If a kitchen range hood, bathroom fan, dryer, or fireplace is running, depressurization can reverse the draft. Test: light a match near the draft diverter — flame should pull toward the chimney. If it pushes away (away from chimney), back-drafting is occurring. Fix by adding combustion air supply.
3. Vent termination height
If anyone recently added a roof addition near the chimney, the termination may now be below adjacent rooflines. Vent must extend 2 ft above any roof surface within 10 ft.
4. Combustion air supply
Tightly sealed mechanical rooms strangle the burner. Code requires 50 cubic feet per 1,000 BTU input. A 40k BTU unit needs a 2,000 cubic foot room or combustion air inlets (two louvered openings sized per code).
Power Vent (6-PVRT) — diagnostic sequence
1. Verify fan operation
On a call for heat, listen for the blower to start. If silent: 120V outlet → blower motor → control board, in that order.
2. Vent termination check
PVC sidewall termination clogged with snow, ice, leaves, or insect nests. Common in winter and spring.
3. Condensate trap
Blocked condensate trap creates back-pressure that the vacuum switch reads as inadequate draft. Clear the trap; verify it\'s primed.
4. Equivalent vent length
If the PVC vent has multiple elbows or runs longer than spec, equivalent length may exceed 40-60 ft. Re-evaluate routing.
Reset procedure
- Address the chimney/vent issue first
- Power-cycle Power Vent units (breaker off 30 seconds)
- Cycle atmospheric gas valve to "Off" for 5 minutes
- Restart and verify LED returns to 1 flash
Bottom line
Atmospheric: inspect chimney → check for back-drafting → verify combustion air. Power Vent: fan running → termination clear → condensate trap. Don\'t bypass the vacuum switch — back-drafting flue gas in living space is a CO hazard.