A Rheem tankless water heater offers hot water on demand, but like any appliance, it can sometimes stop working correctly. One common problem is the Code 12 error. This error can be confusing if you’re not used to troubleshooting tankless water heaters. However, with the right steps, you can often solve it yourself and restore your hot water quickly.
This guide explains what Code 12 means, why it happens, and how to fix it safely. You’ll find clear instructions, practical tips, and key insights to avoid future problems. Even if you have no technical background, you’ll learn how to handle this error with confidence and know when it’s time to call a professional.
Let’s dive in.
What Is Rheem Tankless Water Heater Code 12?
When your Rheem tankless water heater flashes Code 12, it’s telling you something specific: flame failure. This means your unit tried to ignite, but the flame didn’t stay lit or didn’t form at all. The water heater shuts off for safety, stopping the flow of hot water.
This error is common with gas-powered models. While it sounds serious, many causes are simple to fix. Understanding what triggers Code 12 is the first step to a lasting solution.
Main Causes Of Code 12
There’s no single reason for a flame failure. Here are the main causes you should know:
- Gas supply issues – Low pressure, closed valves, or an empty propane tank can prevent ignition.
- Dirty or blocked burner – Dust, insects, or debris can stop the burner from working.
- Ignition problems – Faulty igniters or loose wiring prevent a spark.
- Ventilation blockage – Blocked vents mean the heater can’t breathe.
- Faulty flame sensor – If the sensor is dirty or damaged, the unit won’t detect the flame.
- Electrical issues – Power surges or loose connections can interrupt the ignition sequence.
Many beginners only check the gas supply, but ventilation and electrical connections are often missed and just as important.
Safety Precautions Before Troubleshooting
Before you start, remember that natural gas and electricity are dangerous. Always follow these steps for safety:
- Turn off the power to the water heater at the circuit breaker.
- Shut off the gas supply if you smell gas or suspect a leak.
- Never open sealed parts or bypass safety switches.
- If you’re unsure, call a certified technician.
A small mistake can lead to fire or injury. When in doubt, don’t risk it.
Step-by-step Guide To Fixing Code 12
Ready to solve Code 12? Follow these steps in order, checking after each one to see if the error is gone.
1. Check Gas Supply
A common reason for flame failure is no gas or low pressure. Here’s what to do:
- Make sure the main gas valve is fully open.
- If you use propane, check the tank is not empty.
- Inspect the gas line for any kinks or visible leaks.
- If you smell gas, stop immediately and contact your gas supplier.
2. Reset The Water Heater
Sometimes, an electronic glitch can trigger Code 12. To reset:
- Turn off the heater with the power button.
- Wait 2 minutes.
- Turn it back on.
If the error code clears, it may have been a temporary issue. If not, continue.
3. Inspect The Burner And Flame Sensor
Burners get dirty over time, especially in dusty or insect-prone areas. A dirty burner or flame sensor won’t work properly.
- Remove the front cover (follow your manual).
- Use a soft brush or compressed air to clean the burner.
- Gently wipe the flame sensor with a dry cloth.
- Reinstall the cover and try running hot water again.
Pro tip: Avoid using water or cleaners on the flame sensor.
4. Examine Ignition System
If cleaning the burner didn’t help, check the ignition:
- Listen for a clicking sound when the unit tries to ignite.
- If you don’t hear it, the igniter may be faulty.
- Inspect wiring for loose or disconnected plugs.
- Tighten any loose connections.
Replacing the igniter is a job for professionals. If you suspect this is the problem, call for help.
5. Check Venting And Air Intake
Good airflow is essential for proper ignition. Blocked vents or intakes can cause Code 12.
- Inspect the vent pipe for debris, nests, or blockages.
- Make sure the air intake is free of dust and obstructions.
- Remove any blockages and try the heater again.
Many people overlook venting, but it’s a common cause—especially after storms or renovations.
6. Review Electrical Connections
Loose or damaged wires interrupt communication between the unit’s parts.
- With power OFF, inspect all visible wires and plugs.
- Look for signs of burning, melting, or corrosion.
- Secure any loose connections.
If you find serious damage, don’t try to fix it yourself.
7. Test Water Flow
Tankless water heaters need a minimum flow rate to activate the burner.
- Open a hot water tap fully.
- If the flow is weak, check your home’s water pressure.
- Clean any clogged faucet aerators.
Common Steps At A Glance
Here’s a quick comparison of which problems are most likely and how easy they are to fix:
| Cause | Difficulty | DIY Friendly? |
|---|---|---|
| Gas supply issue | Easy | Yes |
| Dirty burner | Medium | Yes |
| Igniter failure | Hard | No |
| Blocked vent | Easy | Yes |
| Flame sensor issue | Medium | Yes |
| Electrical failure | Hard | No |
Credit: www.afvt.org
When To Call A Professional
You can fix many Code 12 errors yourself, but not all. Contact a certified technician if:
- The error persists after basic checks.
- You find damaged wires or smell gas.
- You’re unsure about any step.
A licensed pro has the tools to check gas pressure, test electronic components, and replace faulty parts safely.
Maintenance Tips To Prevent Code 12
Regular maintenance keeps your Rheem water heater running smoothly and reduces the risk of errors.
Schedule Annual Service
Have a professional inspect and service your heater once a year. They’ll check:
- Burner condition
- Gas pressure
- Venting system
- Flame sensor
This catches problems before they cause a shutdown.
Keep Vents And Intakes Clear
Check outside vents and air intakes every month, especially after storms or home repairs. Remove leaves, nests, or debris right away.
Clean The Burner And Sensor
If you live in a dusty or humid area, clean the burner and flame sensor every 6–12 months. Always follow the manufacturer’s instructions.
Monitor Gas Supply
If you use propane, check tank levels regularly. For natural gas, make sure all valves are open and accessible.
Watch For Unusual Noises Or Smells
Strange sounds or a gas smell are signs of a bigger problem. Don’t ignore them—shut off the heater and call for help.
Credit: www.reddit.com
Common Mistakes To Avoid
Many people make these errors when fixing Code 12. Avoid them for safety and better results:
- Ignoring ventilation – Blocked airways are a top cause of Code 12.
- Forcing ignition – Never try to manually light the burner.
- Skipping regular cleaning – Dust and insects can quickly cause flame failure.
- Over-tightening wires – This can break delicate connectors.
- Resetting too often – Constant resets point to a deeper issue.
Non-obvious insight: Some models have a hidden filter in the gas line or air intake. Check your manual for special cleaning steps.
Understanding Your Model’s Differences
Not all Rheem tankless water heaters are the same. Features, error codes, and fixes can vary by model and year. Always use your model’s manual as your main reference. Here’s a quick comparison of key features:
| Feature | Older Models | Newer Models |
|---|---|---|
| Error Code Display | Lights only | Digital screen |
| Self-diagnosis | No | Yes |
| Flame Sensor Access | Hard | Easy |
| Venting Options | Single | Multiple |
If you’re unsure about your model, find the serial number and check Rheem’s official website for manuals and support.
Cost Of Repair: Diy Vs Professional
Repair costs vary widely. Doing it yourself can save money, but only if you know what you’re doing.
| Repair Type | DIY Cost | Professional Cost |
|---|---|---|
| Clean burner/sensor | $0–$20 | $100–$200 |
| Replace igniter | $40–$80 | $180–$350 |
| Fix vent blockage | $0–$30 | $100–$250 |
| Major electrical repair | N/A | $200–$500 |
Non-obvious insight: Some repairs may void your warranty if not done by an authorized technician. Always check your warranty terms.
Useful Resources
For more details, you can visit the official Rheem support page or consult the Rheem Tankless Support page for model-specific help.
Credit: www.youtube.com
Frequently Asked Questions
Why Does My Rheem Tankless Water Heater Keep Showing Code 12?
Code 12 appears when the burner fails to ignite or the flame goes out. Common reasons are low gas supply, blocked vents, dirty burners, or faulty flame sensors. Addressing each of these areas usually solves the problem.
Is Code 12 Dangerous?
Code 12 is a safety feature. It prevents unburned gas from building up by shutting off the heater if ignition fails. If you smell gas or see repeated errors, turn off the heater and call a professional.
Can I Reset My Rheem Water Heater To Clear Code 12?
You can try resetting the unit by turning it off, waiting 2 minutes, and turning it back on. If Code 12 returns, there’s a real problem that needs attention—it’s not just a glitch.
How Often Should I Clean The Burner And Flame Sensor?
For most homes, cleaning every 6–12 months is enough. If you live in a dusty or humid area, check and clean them more often to prevent errors.
What Should I Do If I Can’t Fix Code 12 Myself?
If basic troubleshooting doesn’t work, or if you find damaged wires, gas leaks, or feel unsure, contact a certified technician. This prevents bigger problems and keeps your home safe.
A Rheem tankless water heater is reliable, but only if it’s well maintained. By understanding Code 12 and following these steps, you can keep your hot water flowing and avoid unnecessary repairs. When in doubt, don’t hesitate to seek professional help—your safety comes first.