Rheem / Ruud Furnace 3 Flashes — Pressure Switch / Inducer Fault
Three flashes on many Rheem/Ruud furnaces indicate a pressure-switch or inducer problem during the call for heat. Treat outdoor vent blockages first, especially after storms or heavy snow.
Updated July 2026 · 5 min read · Canada
Symptoms
- No steady heat; furnace aborts startup
- Status light flashes three times
- Inducer may run without burner ignition
Likely causes
- Blocked PVC terminations
- Failed inducer or pressure switch
- Cracked vacuum hose to the switch
- Severe filter restriction
What to do
1. Inspect and clear terminations
Check both outdoor pipes. Ice, snowbanks, and landscaping screens commonly cause winter 3-flash lockouts.
2. Replace a dirty filter
A packed filter can change cabinet pressures enough to upset sensitive pressure switches on high-efficiency Rheem units.
3. One power cycle, then stop
If vents and filter are good, cycle power once. Repeated resets without a repair waste time and can mask intermittent hose leaks.
Stop and call a pro when
- Code returns with clear vents and a new filter
- You hear grinding from the inducer
- Carbon monoxide detector alarms — leave and call emergency services
Related guides
- Rheem 2 Flashes — Rheem and Ruud 2-flash pressure-switch faults: blocked vents, bad hoses, and inducer issues — with the parts that clear most homeowner-accessible failures.
- Goodman 3 Flashes — Diagnose Goodman (and Amana) furnace LED 3-flash codes: pressure switch, inducer, and flame-sensing failures — plus the parts that usually fix them.
FAQ
Can cold weather alone cause Rheem 3 flashes?
Cold does not directly set the code, but ice and snow blocking terminations is a classic winter trigger.
Need a licensed tech instead?
If the guide says to stop — or the part swap did not clear the fault — get free quotes from licensed local HVAC contractors.
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