Rheem tankless water heater code 13 means the unit shut itself down because it could not correct a combustion problem. Rheem's troubleshooting manual ties the code to the oxygen depletion sensor. Check that the air intake and outdoor vent are clear, reset once, and call a licensed gas technician if the code returns.
Figures checked September 2026. Code meanings from Rheem's use and care and troubleshooting documents; costs from dated sources listed at the end.
| Cause, following Rheem's troubleshooting page | What gets checked | DIY or pro | Typical cost (source, date) |
|---|---|---|---|
| Not enough fresh combustion air, such as a tight closet | Room openings, closet door, intake clearance | DIY to spot, pro to fix | Varies with the fix |
| Manifold gas pressure off | Pressure confirmed and adjusted | Pro, gas-qualified | Service call plus labor (see cost table) |
| Dirt or blockage in the heat exchanger or venting | Vent run and exchanger fins | Pro | $50 to $125 vent repair (Fixr, Jan. 2025) |
| Dirt on the fan motor or the air intake on the front cover | Fan and intake screen | Pro | $50 to $400 maintenance visit (Fixr, Jan. 2025) |
| Blocked flame opening on the sensing burner | Whole burner assembly cleaned | Pro | Part of a service visit |
| Sensor reading low after the checks above | Upper burner assembly replaced | Pro | $400 to $800 burner (HomeGuide, July 2025) |
Code 13 is a safety shutdown after poor combustion that the unit could not fix on its own. Rheem's Tankless Troubleshooting Manual, page 50, describes it as the oxygen depletion sensor being activated because the unit "was not able to resolve an imperfect combustion issue." It is not a simple ignition failure.
The owner-facing chart says much less. In Rheem's Classic Plus use and care manual (AP18000-2 Rev 03, Service Error Code Chart, page 26, page images here), the cause column for 13 reads "If this code is still displayed after taking the numbered steps above," and the solution is to contact a dealer or qualified service technician. The numbered steps it refers to are the reset sequence on page 25.
TanklessHeaterHelp's generic code 13 page calls it a flame failure during operation. Rheem's page does not: the burner can be lit, and the sensor judges the combustion poor.
Code 13 appears on the Classic Plus chart and not on Rheem's current Eagle or condensing charts. A code 13 on your display is a strong sign you own one of the older noncondensing units, so use that manual, not a newer chart, when you look up the fix.
| Product line | Manual (form, page) | Code 13 listed? | Nearby air or vent code |
|---|---|---|---|
| Classic Plus noncondensing | AP18000-2 Rev 03, p. 26 | Yes | 05: air intake or vent exhaust may be blocked |
| Eagle noncondensing | AP22009 Rev 04, p. 77 | No | 90 or 99: air intake or vent blocked |
| IKONIC condensing | AP22745 Rev 04, p. 93 | No (no A013) | A090: air intake or vent blocked |
The Classic Plus manual covers 199,900, 180,000 and 150,000 Btu/h noncondensing models, per its cover, and the manual host files it under RTG-64DVLN-1 and RTG-84DVLN-1. The Eagle manual and condensing manual charts were checked line by line. The rating label settles which chart applies.
Code 05 is the warning; code 13 is the shutdown. On the Classic Plus chart, 05 means the air intake or vent exhaust may be blocked, or the vent pipes may not be connected properly. Rheem's troubleshooting page describes 05 as the step where the board tries to correct the problem itself before it gives up with 13.
That same page, in Rheem's Tankless Troubleshooting Manual, flags one exception. If the sensor produces too little voltage, the board never senses the fault, never tries 05, and simply shuts down. If you saw 05 before 13, the air and vent path is the first place to look.
Close the hot taps, power the unit off at the remote, wait about 5 minutes, and restart. If 13 returns, unplug the unit for about 30 seconds and try once more. Rheem's chart then says to stop and call a technician, not to keep resetting a combustion fault.
The reset sequence is on page 25 of the Classic Plus manual, and the 12-inch intake clearance and intake and vent check are on page 17 of the same AP18000-2 manual.
Fresh air and maintenance history first, then the sensor voltage, then gas pressure, then cleaning and parts. Rheem's troubleshooting page 50 runs as a short flowchart, and a technician only replaces the burner assembly after the other branches check out.
These steps paraphrase page 50 of Rheem's Tankless Troubleshooting Manual. They require the cover off and live power, which is why the owner's manual routes code 13 to a technician.
Some older units were. The CPSC announced a recall on February 21, 2007 of about 42,200 tankless heaters sold under the Paloma, Rheem, Ruud, Rheem-Ruud and Richmond names, including model RTG-74PVN. A shifted air filter door switch could let dust and lint build up, posing a carbon monoxide hazard.
That is the same air-supply path code 13 guards. If your rating label shows a model on the CPSC list, the notice told owners to stop using the heater if the air filter door is not in place and to contact their installer or Rheem for a free on-site repair. The notice is from 2007; confirm with Rheem whether your serial number was already repaired.
Rheem's Classic Plus manual (page 19) warns that skipped maintenance can cause carbon monoxide dangers, tells owners not to run the heater if something seems wrong, and assigns burner, air intake filter and vent inspection to a qualified technician. Page 25 tells owners not to repair gas piping, burners, vent connectors or safety devices. Leave the unit off after a repeat code 13 and call a licensed gas technician. If you smell gas, leave the building and call the gas supplier from a neighbor's phone, as the manual's cover says. Venting basics for gas units are on the gas water heater repair guide.
A cleaning and vent visit sits at the low end; a burner, board or heat exchanger sits at the high end. Fixr (January 2025) lists tankless vent repairs at $50 to $125, and HomeGuide (July 2025) lists a burner replacement at $400 to $800.
| Work | Range | Source |
|---|---|---|
| Service call-out fee | $50 to $200 | HomeGuide, August 2025 |
| Plumber labor | $45 to $150 per hour | HomeGuide, August 2025 |
| Professional maintenance visit | $50 to $400 | Fixr, January 2025 |
| Vent repair, labor included | $50 to $125 | Fixr, January 2025 |
| Vent replacement, labor included | $75 to $250 | Fixr, January 2025 |
| Burner replacement | $400 to $800 | HomeGuide, July 2025 |
| Circuit board replacement | $400 to $800 | HomeGuide, July 2025 |
| Heat exchanger replacement | $600 to $1,300 | HomeGuide, July 2025 |
No dated price for Rheem's upper burner assembly or its oxygen depletion sensor could be confirmed for this guide, so treat the burner row as a general figure. The tankless maintenance cost guide covers what an annual service visit includes.
A defective part may be; a venting or maintenance problem is not. Rheem's residential gas tankless warranty, form TKW-101 (January 2013) covers component parts for 5 years, labor for 1 year and the heat exchanger for 12 years on a single-family home.
Several exclusions in that document line up with code 13 causes:
If there is no proof of the install date, the warranty status is based on the manufacture date from the serial number plus 90 days, per the same warranty form. Terms can differ by model; the certificate in your manual governs. The Rheem water heater repair guide lists warranty terms by product line.
Repair when the cause is air, venting or a cleanable burner; price a replacement when the heat exchanger or several major parts are failing. HomeGuide (August 2025) puts tankless lifespan at 10 to 20 years, and code 13 only appears on Rheem's older noncondensing chart.
| Situation | Better move | Why |
|---|---|---|
| Code 13 cleared after a blocked vent or closet door was fixed | Keep the unit, schedule service | The cause was external |
| Dirty burner or fan, first code 13 in years | Clean and service | Rheem's check list starts with cleaning |
| Sensor or burner assembly failed, unit inside the 5-year parts term | Repair under warranty | Part may be covered; labor term is 1 year |
| Code 13 plus a leaking or sooted heat exchanger on an old unit | Price a replacement | See the tankless replacement cost guide |
For ignition and flame codes on newer models, see the Rheem tankless ignition code guide.
No. On Rheem's charts, 11 and 12 point at the gas supply. Code 13 is a combustion-quality shutdown. The Rheem tankless code 11 guide covers code 11.
Rheem's Classic Plus manual lists the air intake filter under professional preventive maintenance. The owner steps are keeping the intake clear and checking the intake and vent outlet for debris.
A reset does not fix the cause. Rheem's troubleshooting page asks technicians to check maintenance history, because repeat events usually trace to air supply, dirt or a failing sensor.
Rheem's warranty form lists technical service at (800) 432-8373 during Central Time business hours, per Rheem's warranty document, January 2013. Have the model number, serial number and install date ready. Other symptoms are sorted on the water heater problems hub.
Independent Research
Published ranges for tank, tankless and heat pump replacement, the failures that justify a repair, and the ones that do not. Sourced, dated, and free to read.
