Rheem 90 or 99 Error Code: Air intake or vent exhaust may be blocked
Updated October 2026 · Sourced from Rheem documentation
The manual says the air intake or vent exhaust opening may be blocked, or the vent pipes on the vent termination may not be connected properly.
Is it safe to keep running? Check the steps below first. The manual says to contact a dealer or qualified service technician if the vent pipes at the termination may not be connected properly. Turn the heater off and call a pro if the code returns after clearing the blockage.
90 or 99 at a glance
| Code / how it shows | Meaning | Applies to |
|---|---|---|
| 90 or 99 Shown on the LED display of the remote control | Air intake or vent exhaust may be blocked | Rheem non-condensing tankless gas water heaters (160,000, 180,000 and 199,900 Btu/h models) with remote control display |
Check this first
Only steps a homeowner can do safely. Do not open electrical panels or the burner area.
- Look at the outside air intake and vent terminal and make sure nothing (leaves, snow, debris, stored items) is blocking them. The manual says air intake needs 12 inches (30 cm) of clearance.
- Do not open or take apart the vent pipes yourself.
🛑 Stop and call a licensed pro if
- The manual says to contact a dealer or qualified service technician if the vent pipes at the termination may not be connected properly. Turn the heater off and call a pro if the code returns after clearing the blockage.
- You smell gas. Leave the house, do not touch switches, and call your gas utility from outside.
- Codes for flame failure, overheating, venting or the control board that return after one reset.
- Water leaking from the heater, the relief valve discharging, or scorching around the burner area.
- A carbon monoxide alarm sounds. Get everyone outside and call 911 or the fire department.
Safe first steps for any Rheem code
- Write down the exact code shown on the controller or the number of status light flashes.
- Turn the water heater power off and back on (or press the reset button the manual describes) once. If the code comes back, stop resetting.
- Make sure the gas supply valve to the heater is open and other gas appliances in the home are working.
- Make sure the cold water supply valve is fully open and hot water taps are not partly closed.
- Look at the outside vent terminal for snow, ice, leaves or anything blocking it (look only).
Source: Rheem High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual, Service Error Code Chart, p. 77. Codes are series-specific, so your unit's own manual is the final word. Reviewed October 2026.
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