10 Air supply or exhaust blocked / condensate trap full

What the control is telling you

The unit detects restricted combustion air intake or exhaust. On SENSEI and SENSEI RX/CX units, it also triggers when a blocked condensate drain backs up into the internal trap.

Applies to: SENSEI, SENSEI RX/CX and non-SENSEI tankless (condensate trap check: SENSEI and SENSEI RX/CX only)

Likely causes

• Clogged or frozen condensate drain line backing up the internal trap (SENSEI, SENSEI RX/CX)
• Dirty inlet air filter
• Vent installed wrong: unapproved materials, poorly seated or unsealed joints, too long, bad clearances
• Vent pipe crushed by foam sealant, or debris/water/insects inside the vent
• Fan wheel, housing, air duct or check valve restricted or stuck
• Debris in the burner, or blocked heat exchanger fins
• Incorrect altitude parameter, manifold gas pressures or DIP switch settings
• Faulty fan motor/bearing, fan wiring harness or PC Board

Test and repair steps

1. SENSEI/RX/CX Make sure the condensate line drains. A blocked or frozen line backs up into the internal trap and triggers code 10. Then clean the inlet air filter (top right, under the front cover).
2. All Inspect the whole intake and exhaust system inside and out: clearances, approved vent materials for this model, and joints fully seated and sealed.
3. Warning: Never leave the heater running with intake or exhaust disconnected. The next step is a test only. Reconnect the vent right away.
4. All (only if it codes out while you are there): Disconnect the exhaust from the top of the unit and run hot water. If it runs without the code, the restriction is in the vent system.
5. If it still codes out mark each vent joint, take the vent apart and check insertion depth. Reassemble with the vent supplier's lubricant. Bad joints can leak exhaust and cause code 10.
6. Confirm equivalent vent length is within limits (concentric: 90° elbow = 6 ft, 45° = 3 ft). Non-SENSEI: also set the vent-length DIP switches to match.
7. Make sure foam sealant at the wall penetration has not crushed the pipe (check with a flashlight or camera). Open joints and look for water, condensation, insects or debris.
8. Confirm termination clearances to other vent terminals and to overhangs, grade, walls, porches and obstructions, per the venting instructions.
9. Caution: Turn off power. Remove the fan and check the wheel, housing and air duct for restrictions. SENSEI: also make sure the check valve behind the fan is not stuck. Refit the fan and test.
10. SENSEI/RX/CX Confirm the high altitude parameter. Non-SENSEI (gas-qualified only): confirm low/high fire manifold pressures and altitude DIP switches. A wrong setting can trigger code 10 via the burner sensor.
11. Non-SENSEI – WARNING (VE, VA, VB, VC, KA, RH-180, KCM): Turn off power, gas and water. Clear the manifold orifices and burner chamber, then blow out fins at 120 psi (wear glasses/mask) or replace the heat exchanger.
12. SENSEI/RX/CX – WARNING: Turn off power, gas and water before removing the heat exchanger assembly.
13. SENSEI/RX/CX Separate the burner, clean debris from the burner and air chamber, and check the back of the burner. Do NOT blow out the burner with compressed air. Blow out heat exchanger fins at 120 psi or replace.
14. Warning: Disconnect power and gas before replacing parts. Other possible causes: faulty fan motor or bearing, fan wiring harness, PC Board, or wrong DIP switch settings (non-SENSEI).

Settings for these units

RSC supply connection sizes · SENSEI

The PRV and its adapter come in the box; PRV must be rated 150 psi and at least the heater Btu/h.

Condensate drain line must stay at least 1/2 in. over its whole length.

RSC water quality limits · SENSEI

Damage from water above these limits is not covered by warranty.

Hard water should be treated; use the Service Soon (SS) reminder (parameter 03) for flushing intervals.

• RSC clearances to combustibles · SENSEI
• RSC temperature settings available · SENSEI
• RX supply connection sizes · SENSEI RX/CX
• RX water quality limits · SENSEI RX/CX
• RX water treatment and flushing by hardness · SENSEI RX/CX
• RX clearances to combustibles · SENSEI RX/CX

Models that show this code

89 models in Non-SENSEI, RH180 hybrid, SENSEI RX/CX, SENSEI

Other codes on the same units

• 02 Burner did not operate during freeze protection
• 03 Power interrupted during bath fill
• 05 Bypass flow control device fault
• 07 Circulation flow rate below 2.1 GPM
• 11 No ignition
• 12 Flame failure
• 13 Combustion fault
• 14 Thermal fuse or overheat sensor tripped