Rinnai · Tankless Water Heater Serious

99 — Exhaust Blockage / Fan Issue

Indicates exhaust blockage or combustion fan problem — variant of the air/exhaust safety family.

Keep using it?
Limited use only
DIY difficulty
Moderate
Verified against
rinnai.us ↗

How to fix it

  1. Power down and inspect exhaust termination for any blockage.
  2. Trace exhaust vent run looking for sags or disconnections.
  3. Check fan motor — spin freely, no debris.
  4. Verify vent run is within spec for the model.
  5. Replace fan motor if degraded; correct vent installation if non-conforming.

Why it happens

Typical signs: Code 99 mid-operation · Unit shuts off and locks out · Whistling or unusual fan noise

  • Blocked exhaust termination Snow, ice, or debris at cap.
  • Exhaust vent disconnected or sagging Allowing condensate to pool.
  • Fan motor degraded RPM dropping under load.
  • Wrong vent length/diameter Install exceeds spec.

More Rinnai tankless water heater codes

02 02 — Power Interruption / Memory Loss 03 03 — Loss of Communication / EZConnect Issue 10 10 — Air Supply or Exhaust Blockage 11 11 — No Ignition 12 12 — Flame Failure 14 14 — Thermal Fuse / Overheat Cutoff

All Rinnai codes → All tankless water heater codes →

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: rinnai.us.