99 Serious Moderate DIY

Rinnai Tankless Water Heater 99 — Exhaust Blockage / Fan Issue

Rinnai Tankless Water Heater · Error code 99

What 99 Means

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

Symptoms

  • Code 99 mid-operation
  • Unit shuts off and locks out
  • Whistling or unusual fan noise

Common Causes

1
Blocked exhaust termination

Snow, ice, or debris at cap.

2
Exhaust vent disconnected or sagging

Allowing condensate to pool.

3
Fan motor degraded

RPM dropping under load.

4
Wrong vent length/diameter

Install exceeds spec.

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.

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 →

Verified against manufacturer documentation: rinnai.us

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician.