Rinnai Water Heater Error Code 12: How To Fix It


Has your Rinnai water heater been displaying the frustrating “Error Code 12” message? If so, you’re likely feeling confused about what’s causing this error and how to properly fix it. 

Not to worry – this comprehensive guide will provide you with a complete understanding of Rinnai Error Code 12, walk you through potential causes, and detail proven troubleshooting steps to get your unit functioning safely again. 

With simple language and helpful tips, we aim to equip you with the key information needed to troubleshoot this common “no flame detected” error code appearing on your Rinnai tankless water heater

By the end, you’ll know to get your Rinnai water heater back up and running for reliable operation. So, let’s get started! 

What Does Rinnai Water Heater Error Code 12 Mean?

The Rinnai water error code 12 (also known as flame failure code) on your appliance represents a “no flame” failure. 

 What that means in simple terms is that your water heater cannot detect flames in the burner chamber during the ignition cycle (i.e., when it tries to light the burner) or even during normal burner operation. 

You see, your water heater will not be able to heat your water without those flames. And when the heater can’t detect it, it immediately signals it as a problem. Hence the error code 12. 

However, that’s just one way to look at it. The error code 12 could also mean that gas is flowing and there’s ignition (flames), but the unit (or flame rod sensor) is unable to detect it.

Now, remember there are two instances where your flame rod sensor fails to sense flames and triggers the error code 12. Let’s look at those instances in more detail.

Flame Failure During Ignition or Operation

As you already know, the “no flame” error code 12 can appear on your appliance for two different reasons. Grasping what triggers each instance of this error code will prove useful when you want to troubleshoot the problem.

1. During Ignition 

When your burner turns on, gas starts flowing into the burner box and the igniter or spark electrode generates a spark that lights the gas.

Naturally, once the flame is lit, the flame sensor detects it right away. But in cases where it cannot, it results in the error code 12.

Several factors can prevent the flame-sensing rod from detecting the flame such as:

  • Gas flow problems 
  • Ignition component failure (or faults)
  • Flame rod issues
  • Debris interference 
  • Installation of an incorrect venting material for your hot water unit
  • Moisture in the tube connecting the gas combustion chamber to the gas solenoid valves

2. During Operation

Sometimes, the problem doesn’t happen during Ignition and that’s because the flame rod sensor was able to register flames at the start.

But if for any reason during operation, it fails to register a flame signal, it can trigger the error 12 code.

The error 12 code can be triggered during operation as a result of:

  • Intermittent gas supply problems 
  • Contamination of the flame rod
  • Damaged flame rod
  • Damaged flame rod wires
  • Loss of flame rod electrical connectivity 
  • Unexpected unit shutdown 

In all, the code 12 appearing on your appliance simply indicates that your water heater can no longer detect or determine if there is a burning flame. Specifically, it is triggered by the flame monitoring system. 

How to Fix Rinnai Code 12

Now you know what the Rinnai water error code 12 is and why it’s appearing on your unit. Since you have a firm understanding of the problem at hand, let’s look at different detailed troubleshooting steps you can take to resolve the issue.

1. Check gas supply and connections

When you see your Rinnai water heater showing the error code 12 for the very first time, the first thing you should do is inspect the external gas supply lines or gas meter feeding gas into the unit.

You can quickly verify if your unit is receiving proper gas flow by doing the following:

Step 1: Ensure gas is turned on and supplied to the unit

The first thing you should do when you notice the error 12 code on your unit is confirm whether the Rinnai’s manual shut-off valve is in the open or “on” position. 

While you are at it, also check to see if the upstream shut-off valves located at the branches, quick connections, or main gas line are fully open.

Don’t know where to look? You can find them on your external unit, at the meter, or the main interior gas line connection. 

If your unit is propane-fed, the approach you’d take is a bit different.

For propane-fed Rinnai units, visually check the large external tank (cylinder) to ensure that the primary shut-off valve is properly positioned to allow fuel flow from the tank – also confirm if there’s enough gas in the gas tank. 

Alternatively, the gauge on the tank itself should help you confirm whether your unit is receiving adequate gas pressure and supply. 

Step 2: Check for gas leaks   

Once you are done with the first round of inspection, comes another round of inspection. But this time, you’ll be checking for potential gas leaks in the gas piping system using a commercial leak detector solution or an electronic gas sniffer tool. 

To properly carry out this inspection, start from all the joints and connections from the unit’s back to the point of supply.

Key areas you should focus on include fittings, elbows, tees, transitions, shut-off valves, flanges, and pipe threads. On tanks, check valve fittings and pipe connections at the withdrawal point.

Once you are done with the inspection, if you notice leaks anywhere, seal them before moving on to step 3.

Step 3: Verify adequate gas line sizing and pressure

For this step, start with making sure that the installed gas piping type and diameters align with the specifications for your Rinnai model (reference your installation manual).

Doing this will ensure that your unit will be able to receive enough gas when it is being run under full-demand conditions. 

Once that is out of your checklist, use a digital manometer to check the live dynamic inlet gas pressure reaching your unit when it’s being operated at high fire.

On your unit, the gauge port connector will be located on the side of the unit marked for inlet pressure. 

Now compare the measured operating pressure to the listed minimum inlet requirement needed for proper operation on your manual.

If your reading was below the minimum required, you’ll have to upgrade your gas line sizing.

2. Inspect flame rod

Throughout this article, we have made mention of the flame rod. What’s the flame rod anyway? The flame rod component is a thin metallic device positioned within the burner flame profile (i.e., within the burner cover).

Its sole job is to detect the presence of flame and enable heating functionality. 

Since it’s a core flame monitoring apparatus, it totally makes sense to check it as well.

Step 1: Check for tightness 

The first thing to do is to check if the ceramic flame rod is securely fixed in its mounting bracket within the combustion chamber. You’ll know it’s loose if the tip shifts away from the flame source. 

In this case, gently attempt to wiggle the base of the rod with your hand to check for play or movement. A tight threaded mounting will prevent motion.

Step 2: Clean the flame rod of debris/carbon build-up  

If there’s any soot, oxidation, or scale build-up on the ceramic flame rod insulator, you’ll have to remove the rod from its bracket. When removing the rod, pay close attention to how the rod is being attached to the bracket and remember its position and angle – if you think you might forget, take a picture of it. 

After successfully detaching the rod, polish away the contamination using a very fine grit emery cloth or a synthetic scrub pad until the ceramic surfaces become smooth again.

Cleaning the rod prevents insulation and ensures full contact with the micro-amp flame signal. 

After cleaning, properly place the rod in its correct position – this is where your memorization skills or the picture will come in handy.

Note: Be careful during the cleaning process so you don’t end up damaging the flame rod surface. Also, clear any debris you may find under rod mounting before mounting the rod.

Step 3: Replace flame rod gasket  

The flame rod has a high-temp gasket ring that helps in securing it on the burner mounting. Check the ring for any signs of cracking or compression wear. Cracked or worn rings can allow combustion gases to bypass and blow out the flame signal. 

A foolproof method you can employ is changing the ring every time you take out the rod. This way, you’ll be sure that the ring is never compromised.

3. Clear blockages

Beyond fuel supply and a properly functioning flame rod, error code 12 can also appear when debris physically blocks internal gas flow paths or interrupts signal transmission. With that in mind, here are some troubleshooting steps to carry out:

Step 1: Remove and clean burners

Remove the burner plate and inspect all individual burner cups as well as passages underneath them for dust, lint contamination, or spider/insect nesting. If present, thoroughly clean all foreign material buildup using compressed air.

When clearing, ensure that all port holes across the burner surface are widely patent (i.e., ensure they are fully open). 

Note: When cleaning, avoid scraping burners because it can leave scratches and the scratches may impact the combustion performance. Also, if you notice heavy oxidation that you are unable to brush or wipe away, prime and paint the burners.

Step 2: Clear debris from heat exchanger fins

Look into the stainless-steel heat exchanger using a bright flashlight. Search for any accumulated fibrous debris or other combustible material packed between interior fins that are capable of narrowing the vital airflow channels.

During inspection, if you notice any, you should blow out your heat exchanger. For that, you’ll need to use “high-pressure shop air” (compressed air) regulated to approximately 120 PSI to forcefully eject clogs. 

Your safety is always important, so if you must do this, wear eye protection and avoid facing the open exchanger directly to avoid blowback injuries or burns.

If needed, you can also change the burner box orientation so you can gain more access to restricted areas during the cleaning process.

Step 3: Check/clean the fan blower wheel 

Check the blower fan blades and housing for any buildup of debris like lint networks or insect residue inside the burner air intake flow path leading to the combustion chamber. 

If you find obstructions, you can try to remove large accumulations by hand initially then detail clean the entire fan wheel, shaft, and venturi opening using pressurized air if need be. Do well to ensure that no sticky buildup remains on the fan blade to impair rotation or disturb airflow.

4. Fix venting issues

The exhaust vent terminal is responsible for the safe transportation of combustion byproducts outside the unit. This very important vent plays a major role in the flame consistency and the proper functioning of the burner ignition.

If something should go wrong with the exhaust, it will affect the unit and, in some cases, lead to the “no flame” error 12 code. Here are the things you can try to troubleshoot this problem:

Step 1: Ensure proper venting materials used

Go through all the vent components and piping, including the condensation collar, to see if they comply with your Rinnai’s water heater exhaust venting specifications, including approved pipes, terminations, elbows, and seals and connections. 

For stainless steel concentric dimensioned vent bodies, make sure to check or confirm if the dimensioned tolerances fall between 3 to 5-inch diameter of the diameter of your sizing unit’s model requirements.

An improper vent piece can lead to the error 12 code.

Note: The venting installations for open-air external applications may allow some flexibility but all indoor venting of tankless Rinnai products must use certified Category IV materials resistant up to 480°F exhaust temperatures. 

Step 2: Check for blockages or leaks

Next, you’d want to remove the vent sections from the top down and visually inspect the inside runs for accumulation of debris, nesting residues, or condensed moisture pooling at low points that are capable of obstructing free exhaust flow.

Also, check if the external wall or roof caps have a venturi clearance all around. For the fix, you can repair joints that are separating, or you can go ahead to replace defective parts that are permitting combustion gas leaks.

Step 3: Verify clearances

For this step, make sure that clearance distances around external wall or roof terminations meet minimums per the installation guide to prevent exhausted combustion gases from recirculating back into intake air feeds. 

Here, a quick fix might require you to use an extension kit to shift the vent exhaust exit point outward if feasible. 

5. Replace moisture-damaged parts

Despite your best efforts to curb or prevent this error code, leak pathways or chronic condensation within the unit can still contribute to loss of flame detection causing code 12. 

Here are some primary reasons associated with moisture-damaged parts and how to resolve them:

Replace the Gas valve and Heat Exchanger 

Some internally installed Rinnai models use plastic tubing to channel combustion byproducts down from the flame chamber to the gas control valve below.

Do well to thoroughly Inspect this narrow ventilation tubing path for any droplets or accumulation of moisture that must have drained from above. 

If you notice significant water presence, it most likely means there’s a leak point in the heat exchanger seals above that allows exhaust gases to mix into the air feeds.

It also indicates that the gas valve has failed to properly meter and deliver fuel. 

In such situations, replacing the heat exchanger or the gas control valve will restore your burner’s performance and clear the error code.

6. Confirm the proper electrical operation

When troubleshooting the error code 12 in your Rinnai water heater, it’s important to ensure that the electrical flame-sensing circuit is working properly, and that the appliance is properly grounded. 

Step 1: Check the wiring harness for damage

High temperature, vibration, and moisture can degrade wires over time. Closely look at the factory wiring harnesses spanning from the internal burner enclosure out to PCB controller connections for any cuts, nicks, brittle segments, separated connectors, or overheating signs. You can use a bright flashlight for the inspection. 

Gently handle the harnesses while observing wire or connector motion at interfaces and junction terminals – they could reveal loose connections or intermittent contact issues. After your observation, tightly secure any loose screw terminals.

Note: For damaged or defective wire segments you need to replace them – don’t try to repair them. 

Step 2: Ensure proper electrical grounding 

Use a multimeter to measure the resistance between your unit’s ground points and the earth’s ground. What you should expect here is a zero value and that value means that the ground wire is good – it is not damaged by rust or loose ends.

Also, check to see if the third prong on the plug is connected to the same ground points.

Step 3: Replace the PC board if needed

If your inspection reveals that there are no home run wiring or component defects, then the controller electronics may be the culprit. 

Monitor gas valve signal voltages through the ignition sequence during a new heating cycle attempt to assess for proper activation timing and levels.

Intermittent or out-of-specification valve activation voltage often requires the replacement of the entire PCB controller to restore normal function. 

How to Prevent Rinnai Water Heater Error Code 12

It is often better to prevent something than to fix it. If you have tried the troubleshooting tips in the “How to Fix” section, then there’s a high chance you have fixed the problem. And it’s now time to ensure you never encounter the problem again.

Here are some tips to help you avoid the problem in the future:

Cleaning and inspection schedule 

Create a biannual schedule for a qualified technician to thoroughly inspect the key components influencing reliable flame detection. 

Note: More frequent maintenance cycles may be warranted in areas with poor water quality. Keep the records of maintenance checks. 

Flushing heat exchanger

To stop or prevent scale from building up inside your heat exchanger and blocking it, turn off the water supply and flush the heat exchanger using an approved descaling solution concentrated with citric acid to remove mineral adhesions.

After flushing, rinse it to neutralize pH.

Water treatment to prevent scale buildup

Use a residential water softener or hard water treatment chemicals in your home’s water to reduce dissolved mineral solids. This will help in stopping the water from making hard deposits.

Polyphosphates can help stop the minerals from sticking together. So you can consider using that too. In all, just try to keep the water hardness under 120 ppm.


We hope this guide has helped you better understand Rinnai water heater error code 12 – what causes the “no flame detected” failure and the systematic steps you can take to resolve it. 

While troubleshooting, be sure to carefully follow all safety protocols when handling gas lines or replacing parts. If at any point the repair seems unsafe or you lack the proper tools, don’t hesitate to call in a licensed technician. 

Remember, early intervention when you first notice error code 12 can help mitigate serious secondary damage needing costlier replacements down the road. 

Be proactive with preventive maintenance too – flushing minerals, descaling the heat exchanger, monitoring combustion airflow paths, and vent exhaust. This will go a long way to optimize the performance and lifecycle of your Rinnai.

Related Articles: Tankless Water Heater Goes Cold After a Few Minutes

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