Rheem Tankless Code 29: Condensate/Neutralizer Fault

Rheem tankless code 29 points to a fault in the condensate drainage or neutralizer system — the parts that safely dispose of the acidic condensate a high-efficiency gas unit produces. A clogged drain line or a full/blocked neutralizer cartridge is the usual cause.

Illustration of a condensate neutralizer cartridge filled with limestone pellets, mounted beside a tankless water heater.

Likely Causes, Ranked

Clogged condensate drain line
Sediment or algae buildup over time is common, especially on a line with poor slope.
Blocked or exhausted neutralizer cartridge
If your install uses one, it needs periodic replacement.
Condensate trap dried out or improperly primed
Can allow pressure imbalance that the sensor reads as a fault.

Step-by-Step Diagnosis

DIY SAFE
Inspect the condensate drain line for visible clogs or kinks

Follow it from the unit to wherever it drains.
DIY SAFE
Check the drain line slope

It should run continuously downhill — a sagging section can trap water and sediment.
DIY WITH CAUTION
If a neutralizer cartridge is installed, check/replace its media

Follow the manufacturer’s replacement interval.
PRO ONLY
If the line and cartridge check out and the code returns

Have a technician check the condensate sensor and trap.

FAQ

What is a neutralizer cartridge and do I have one?

It’s a small cartridge some high-efficiency gas units use to neutralize acidic condensate before it drains — check your install manual or look near where the condensate line exits the unit.

Related guides: Rheem Tankless Error Codes

Written by HotWater Decoded — water heater repair specialists. Technically reviewed by a licensed technician on our team.

Sources

General condensate-fault pattern on high-efficiency gas tankless units, cross-referenced with symptom reports