Rheem Tankless Code 10: Air Supply or Exhaust Blockage Warning (Meaning, Causes, Fixes)

What the code means

Rheem's High and Super High Efficiency Tankless Troubleshooting Manual (AP21822) lists 10 as a Warning Code, Incorrect inlet air volume. Rheem explains that the heater shows 10 on the built-in or remote controller if it was operated before the venting was installed, or if the blower motor isn't creating enough ventilation. The manual's two check items are the venting and the blower motor: check the vent connections and the termination, and if the venting is disconnected or the termination is blocked, reconnect the vents or clean the termination on both the inlet (air intake) side and the exhaust side. If the venting is fine, Rheem sends the technician to its code 61 procedure for the blower (blower motor speed incorrect for combustion), which checks the blower connector, voltages and RPM signal and ends in replacing the control board and/or blower. Rheem's Technical Service Bulletin for RTG 74 tankless fault codes (indoor, outdoor and heavy duty models) describes 10 as a warning or predictive code, not a fault code, for an air supply or exhaust blockage, with remedies to check all vent components for proper connections, make sure nothing blocks the flue inlet or exhaust, confirm the condensate trap and drain were installed correctly, and make sure the heat exchanger fins, fan and air intake aren't blocked. Because it is a warning, the heater may keep running while 10 is showing, but the blockage behind it can turn into ignition or combustion error codes if it gets worse.

Likely causes

• A blocked vent or air intake termination outside, such as leaves, a nest, snow, ice or debris (Rheem says to clean both the inlet and exhaust side)
• A vent pipe that is disconnected, loose or crushed somewhere along its run
• The heater being run before its venting was installed, which Rheem names directly
• A condensate trap or drain that wasn't installed correctly, letting water back up (condensing models, per Rheem's fault code bulletin)
• Dust or lint blocking the air intake, combustion fan or heat exchanger fins
• A blower motor that isn't moving enough air, which Rheem checks with its code 61 blower procedure

Safe DIY checks

1. Write down the code and your model number from the rating plate.
2. Go outside and look at both vent terminals, the air intake and the exhaust. Clear leaves, nests, snow, ice or anything stacked near them. Rheem says to clean both sides.
3. Follow the vent pipes you can see from the heater to the wall or roof and check that every joint is still connected and no pipe is crushed or sagging.
4. On a condensing model, check that the condensate drain line isn't kinked, clogged or frozen and that it drains freely.
5. If the heater has an air intake screen or filter you can reach without opening the sealed combustion section, check it for lint or dust and clean it as your manual describes.
6. Then run hot water and see whether 10 clears. If it keeps coming back with clear vents, or if you see other codes like 11 or 61 along with it, call for service.
7. Don't open the sealed combustion section or modify the vent pipes yourself. If you smell gas, leave the house and call your gas utility from outside.

Parts that commonly fix it

Always match the part number to your exact model.

Related codes

• 12 Rheem Tankless Water Heater 12
• 13 Rheem Tankless Water Heater 13
• 14 Rheem Tankless Water Heater 14
• 29 Rheem Tankless Water Heater 29
• 45 Rheem Tankless Water Heater 45

All Rheem codes →

Sources

1. Rheem High and Super High Efficiency Tankless Water Heater Troubleshooting Manual AP21822, page 38 (10 Warning Code: Incorrect inlet air volume, shown if operated before vent installation or blower not creating enough ventilation; check vent connections and termination, clean both inlet and exhaust side; blower per 61 Error Code section) and page 51 (61 Error Code blower check)
2. Rheem Technical Service Bulletin, RTG 74 Tankless Fault Codes (Indoor, Outdoor and Heavy Duty models): 10 Warning or Predictive Code, not a fault code, Air Supply or Exhaust Blockage (vent connections, flue inlet and exhaust, condensation trap/drain, heat exchanger fins, fan and air intake)