Rheem Tankless Gas Code 29
Condensate not draining, or heat exchanger too cold. Rheem documents this code in two parts. On high-efficiency (condensing) units only, part A means condensation is not draining — and its listed causes are almost all installation faults: the plug never removed from the condensate drain, a pinched or blocked drain line, or an unnecessary P-trap in it. Part B, which applies to both mid- and high-efficiency units, means the heat exchanger temperature was too low for more than three minutes.
Call a proThe verdict
Call a licensed plumber
If your unit is condensing, start with the condensate drain — Rheem does, and the causes it lists are things an installer either did or did not do. What you can check from outside is whether the drain line is kinked, blocked, or frozen. The rest, including part B's thermistor and gas valve checks, is a service call.
Typical cost: $0–$900
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the Tankless Gas — not averaged across the brand.
Source: Rheem Tankless Gas Troubleshooting Pocket Manual (SVC820) (p. 55), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
Before anything else: if you smell gas, stop here, leave, and call your gas utility.
- Follow the condensate drain line and check it is not kinked, blocked, or frozen where it leaves the building.
- If the unit was installed recently, ask the installer whether the condensate protection plug at the bottom of the unit was removed — Rheem lists that as cause number one.
- Do not add or remove traps on the drain line yourself; Rheem specifically flags an unnecessary P-trap as a cause.
- If the drain is clear and the code stays, book a licensed professional.
Frequently asked questions
How do I know whether my unit is condensing?
A condensing (high-efficiency) unit produces liquid condensate and has a drain line for it, plus an acid neutralizer. If there is no condensate drain, part A of this code does not apply to you and part B does.
A plug left in the condensate drain — really?
It is the first thing Rheem lists. Units ship with a protection plug at the bottom that has to be removed and the drain connected during installation. If it was missed, condensate has nowhere to go from the day it was fitted.