What causes Rheem Tankless Water Heater 29?

The protection (shipping) plug was never removed from the condensate drain connection at the bottom of the unit (common right after installation). A pinched, kinked or clogged condensate drain line. An unnecessary P-trap added to the drain line (Rheem says the unit has its own built-in trap, so the line doesn't need one). Clogged drainage ports inside the neutralizer or a blocked neutralizer drain line outside the unit. A wet or faulty water-level electrode in the drain trap. On mid-efficiency and some older units: low heat exchanger temperature from a dirty air inlet screen or dirty heat exchanger fins.

How do I fix Rheem Tankless Water Heater 29?

Do Rheem's reset: turn off all hot water faucets, turn the heater off with the POWER ON/OFF button, wait about 5 minutes, turn it back on, then open a hot faucet and check the display. If the code is still there, turn the faucet and heater off, unplug the heater for 30 seconds, plug it back in and repeat. Follow the condensate drain hose from the bottom of the heater to where it empties. Straighten any kinks or pinches, and make sure the far end isn't blocked, buried in debris, or frozen. If the heater was just installed, check that the plastic protection plug was removed from the condensate drain connection at the bottom of the unit. If someone added a P-trap (a U-shaped loop) in the condensate line, tell your installer; Rheem says the line doesn't need one, and it can hold water back. Condensate is acidic. Wear gloves if you handle the drain hose, and don't route it anywhere other than a proper drain. Don't open the heater's cover. Cleaning the neutralizer ports, the drain trap and the water-level electrode is service work, and Rheem's installation guide tells owners to contact a dealer or qualified technician if 29 stays on.

When should I call a pro for Rheem Tankless Water Heater 29?

Confirming the drain-connection protection plug is removed and the condensate line has no internal or external blockage, pinch or unneeded P-trap. Clearing all neutralizer drainage ports inside the unit and the neutralizer drain line outside it. Checking the neutralizer water-level electrode and making sure it isn't wet. Cleaning the air inlet screen and heat exchanger fins when the cause is low heat exchanger temperature. On older non-condensing units (SVC 810): verifying heat exchanger temperature in maintenance mode, measuring the heat exchanger thermistor (about 4k to 10k ohms between the black #3 and yellow #5 wires on connector R), then replacing the thermistor or control board as indicated.

Code: 29🚿 Rheem Tankless Water Heater

Rheem Tankless Water Heater Code 29: Condensate Not Draining (Meaning, Causes, Fixes)

Q: What does Rheem Tankless Water Heater 29 mean?

Code 29 on a Rheem high-efficiency (condensing) tankless water heater means condensate isn't draining out of the unit's built-in drain trap or neutralizer. The usual causes are a shipping plug left in the drain connection, a kinked or clogged condensate line, or an unneeded P-trap on the drain line. On some older mid-efficiency Rheem models, 29 instead means the heat exchanger temperature is too low. Rheem's High and Super High Efficiency Tankless Water Heater Troubleshooting Manual (AP21822) calls 29 "Condensation not drained from collector." These condensing models have a built-in drain trap with an electrode in it; if the electrode senses the trap is full of water, or can't detect the water level at all, the control shows 29 and stops heating. Rheem's tankless installation guide words it for owners as "Condensation Trap is clogged." Rheem's older SVC 820 service manual lists the same code as "Condensing Only: Neutralizer is clogged" and "Condensate Drain is NOT draining," and gives a second meaning on mid-efficiency and condensing units: heat exchanger temperature too low, usually from a dirty air inlet screen or heat exchanger fins. The SVC 810 manual for older non-condensing models such as the RTG2-42 lists 29 only as "Heat Exchanger outlet temperature is too low." Code 29 isn't in the service error-code chart for Rheem's non-condensing Eagle tankless models.

Reviewed 2026-10-23 · Based on 5 manufacturer & service sources

What the code means

Rheem's High and Super High Efficiency Tankless Water Heater Troubleshooting Manual (AP21822) calls 29 "Condensation not drained from collector." These condensing models have a built-in drain trap with an electrode in it; if the electrode senses the trap is full of water, or can't detect the water level at all, the control shows 29 and stops heating. Rheem's tankless installation guide words it for owners as "Condensation Trap is clogged." Rheem's older SVC 820 service manual lists the same code as "Condensing Only: Neutralizer is clogged" and "Condensate Drain is NOT draining," and gives a second meaning on mid-efficiency and condensing units: heat exchanger temperature too low, usually from a dirty air inlet screen or heat exchanger fins. The SVC 810 manual for older non-condensing models such as the RTG2-42 lists 29 only as "Heat Exchanger outlet temperature is too low." Code 29 isn't in the service error-code chart for Rheem's non-condensing Eagle tankless models.

Likely causes

The protection (shipping) plug was never removed from the condensate drain connection at the bottom of the unit (common right after installation)
A pinched, kinked or clogged condensate drain line
An unnecessary P-trap added to the drain line (Rheem says the unit has its own built-in trap, so the line doesn't need one)
Clogged drainage ports inside the neutralizer or a blocked neutralizer drain line outside the unit
A wet or faulty water-level electrode in the drain trap
On mid-efficiency and some older units: low heat exchanger temperature from a dirty air inlet screen or dirty heat exchanger fins

Safe DIY checks

⚠ Before you start

Unplug the appliance (or switch off its breaker) and shut off the water supply valves before removing panels or disconnecting hoses. Keep towels handy for residual water.

Do Rheem's reset: turn off all hot water faucets, turn the heater off with the POWER ON/OFF button, wait about 5 minutes, turn it back on, then open a hot faucet and check the display. If the code is still there, turn the faucet and heater off, unplug the heater for 30 seconds, plug it back in and repeat.
Follow the condensate drain hose from the bottom of the heater to where it empties. Straighten any kinks or pinches, and make sure the far end isn't blocked, buried in debris, or frozen.
If the heater was just installed, check that the plastic protection plug was removed from the condensate drain connection at the bottom of the unit.
If someone added a P-trap (a U-shaped loop) in the condensate line, tell your installer; Rheem says the line doesn't need one, and it can hold water back.
Condensate is acidic. Wear gloves if you handle the drain hose, and don't route it anywhere other than a proper drain.
Don't open the heater's cover. Cleaning the neutralizer ports, the drain trap and the water-level electrode is service work, and Rheem's installation guide tells owners to contact a dealer or qualified technician if 29 stays on.

🛠 When to call a pro

Confirming the drain-connection protection plug is removed and the condensate line has no internal or external blockage, pinch or unneeded P-trap.
Clearing all neutralizer drainage ports inside the unit and the neutralizer drain line outside it.
Checking the neutralizer water-level electrode and making sure it isn't wet.
Cleaning the air inlet screen and heat exchanger fins when the cause is low heat exchanger temperature.
On older non-condensing units (SVC 810): verifying heat exchanger temperature in maintenance mode, measuring the heat exchanger thermistor (about 4k to 10k ohms between the black #3 and yellow #5 wires on connector R), then replacing the thermistor or control board as indicated.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Condensate drain hose or tubing

Only if the existing line is cracked or kinked beyond straightening; match your installer's size and route.

[affiliate link slot: AFFILIATE_SLOT_CONDENSATE_HOSE]

⚙

Plug-in carbon monoxide alarm with digital display

Worth having near any gas water heater.

[affiliate link slot: AFFILIATE_SLOT_CO_DETECTOR]

⚙

Rheem tankless neutralizer (exact part for your model)

Technician part only, if the neutralizer can't be cleared.

[affiliate link slot: AFFILIATE_SLOT_CONDENSATE_NEUTRALIZER]

Sources

Last reviewed 2026-10-23. Always confirm against the manual for your exact model number.

Rheem Tankless Water Heater Code 29: Condensate Not Draining (Meaning, Causes, Fixes)

What the code means

Likely causes

Safe DIY checks

🛠 When to call a pro

Parts that commonly fix it

Condensate drain hose or tubing

Plug-in carbon monoxide alarm with digital display

Rheem tankless neutralizer (exact part for your model)

Related codes

Sources