Rheem Tankless Water Heater Troubleshooting
On this page (6 sections)
The Short Answer: When a Rheem gas tankless stops heating, work through four things: power to the unit and remote, enough water flow to switch it on, a clean inlet water filter, and any error code on the remote. Rheem’s RTG manual lists owner fixes for several codes, such as opening the gas valve fully for 11 and clearing a blocked vent for 90 or 99. Anything beyond those needs a technician.
Start with the remote display
| What you see | Likely area | Where to go next |
|---|---|---|
| Remote completely blank | No power: unplugged, tripped breaker or GFCI, or a remote problem | Check power |
| Remote on, no code, water stays cold | Not enough flow to activate, or a clogged filter | Check flow and filter |
| A code is displayed | The heater has detected a specific fault | See the code table below |
| Hot, then cold during a shower with no code | Low flow at that fixture, or mixing at a faucet | See tankless goes from hot to cold |
| Water inside or under the unit | Leak | See Rheem tankless leaking inside |
Flow and the inlet filter
A tankless heater only fires when water flows through it fast enough. For the RTG models in Rheem’s Use & Care manual (opens in a new tab), the minimum activation flow is 0.4 gallons per minute. A single faucet barely open, a clogged aerator, or a partly closed isolation valve can keep the heater from starting.
The manual also has owners clean the water filter on the cold inlet monthly. A clogged filter cuts flow and can stop the heater from activating. The manual describes turning off power and water, draining the unit, unscrewing the filter, rinsing it, and refitting it without overtightening. If you aren’t comfortable with that, it’s a quick job for a technician.
Codes from the RTG manual
| Code | Rheem’s listed cause | Rheem’s listed remedy |
|---|---|---|
| 11 | Gas shut-off valve not fully open | Open it completely; see Rheem tankless flashing 11 |
| 12 | Gas service interrupted, or LP running low | Contact the gas utility or refill LP; see Rheem tankless code 12 |
| 14 | Water heater overheating | Contact a technician |
| 1L | Lime (scale) buildup | Contact a technician |
| 88 | Reminder to flush the heat exchanger or replace the water treatment filter | Contact a technician |
| P1 | Not enough water flow | Increase flow from the fixtures |
| 90 or 99 | Air intake or vent blocked, or vent pipes not properly connected | Remove the blockage; keep 12 inches clear in front of the intake; otherwise call a technician |
| 31, 33, 61, 66 | Sensor, blower, or bypass motor fault | Contact a technician |
Other Rheem tankless lines, including condensing IKONIC models, use different codes. Check the manual for the model on your rating plate.
Rheem’s reset steps
When a code appears, the manual says to turn off hot faucets, turn the heater off at the remote, wait about five minutes, turn it on, and try a hot faucet. If the code is still there, turn the heater off, unplug it for about 30 seconds, apply the chart remedy, and try again. If it still shows, write down the code and call for service. If a code isn’t in the chart, turn the heater off and call for service.
What the technician will check
A technician will check gas pressure under full fire, ignition and flame sensing, the blower and venting, and the temperature sensors. For 1L, 14, or 88, they flush the heat exchanger with the service valves and look at whether water treatment is needed.
Frequently Asked Questions
Q: How often should a Rheem tankless be flushed? A: It depends on water hardness. Code 88 is the heater’s reminder, and 1L means scale is already building. A technician can recommend an interval for your water.
Q: Why does my Rheem only heat when I open the tap fully? A: Flow below the activation threshold won’t start the burner. Clean aerators and the inlet filter, and make sure isolation valves are fully open.
Q: Is a Rheem tankless reset the same as a Rheem tank reset? A: No. Tank heaters use a gas-control status light or, on electric models, a high-limit reset. The tankless resets by turning it off and on at the remote as the manual describes.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- Rheem: RTG non-condensing tankless Use & Care manual (AP22009) (opens in a new tab)Rheem RTG-70/84/95DVL-3 direct-vent and outdoor non-condensing tankless models; other Rheem tankless lines have their own manuals.
- Rheem: owner help and support (opens in a new tab)Identify the applicable model instructions or contact Rheem support.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
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