5 Common Rinnai Tankless Water Heater Problems and Error Codes

Tankless water heaters are a smart investment for any homeowner. They are long-lasting and they allow you to get hot water quickly without taking up too much space. Still, even the best brands might experience some issues. Even Rinnai tankless water heater problems are bound to happen sometimes.

Rinnai is one of the oldest gas appliance companies in the world. While it started by manufacturing pressurized oil stoves, it quickly started producing appliances such as gas heaters and gas ovens. It is also one of the best known manufacturers of energy-efficient tankless water heaters.

Rinnai’s products can last for decades if taken care of properly. Still, any water heaters can experience issues after a while or if you didn’t maintain them the right way.

Here are some of the most common Rinnai tankless water heater problems you might run into, as well as troubleshooting help:

Most Common Rinnai Tankless Water Heater Problems


Rinnai tankless water heater problems are not that different from problems you might experience with any other brand of water heaters. Whether you’re having Rur or Ru model of Rinnai water heater, the issues will usually come down to this:

  • Mineral buildup
  • Ignition failure
  • Flame failure
  • Exhaust blockage or air supply blockage
  • Cold water sandwich

Here’s what you can do about it:

Mineral buildup

Mineral buildup is probably the most common problem any water heater experiences. While there are many pros to tankless heaters, none of them are immune to hard water.

In fact, tankless water heaters are more prone to harmful mineral buildup as the buildup cannot occur in tanks. Instead, it will occur on some of the main elements the unit needs for functioning.

The main minerals causing problems are magnesium and calcium, as they cause scaly buildup that can damage your water heater.

Unfortunately, there isn’t a single code on your Rinnai water heater that will clearly let you know you’re dealing with mineral buildup. While the Error Code 00 or LC lets you know there is buildup in heat exchanger, many other codes might also indicate the same issue, but only in different location.

The buildup can cause most elements to malfunction, so this is something you need to investigate no matter what code you get.

The first thing you need to do if you’re suspecting mineral buildup is to check the filter. This is especially important if you use well water, as it can carry debris that can block the pipes.

The best solution for mineral buildup is to regularly flush your water heater. If you allow the buildup to be too prominent, a professional might even advice you to replace your water heater before it fails entirely.

Ignition Failure

If you notice your water heater not heating water and you see the Error Code 11 on the screen, you are dealing with ignition problems.

There are many reasons why this might’ve happened. Most of the time, it has to do with the gas supply. Check out whether your water and gas valves are fully opened and if your propane tank is full.

If nothing helps, your only solution is to call a professional. You don’t want to deal with gas lines without someone who knows what they are doing.

Flame Failure

Flame failure is marked with the Error Code 12. This is yet another serious issue, and you shouldn’t mess too much with the components that are causing these Rinnai tankless water heater problems.

There are some things you can do to rule out some of the simple causes. For example, you might have simply forgotten to pay your gas bill or to fill your gas tank!

Some other reasons behind flame failure might be:

  • Too small gas line
  • Combustion issues
  • Improper venting
  • Regulator failure

Unfortunately, these problems are usually too much for novices to handle. You need to call a professional who can help you with this.

Exhaust Blockage or Air Supply Blockage

If you see Error Code 10, chances are you’re dealing with blocked exhaust or air supply. As you might’ve guessed, this means that your tankless water heater is having problems with venting or combustion air.

The first thing you need to do is check vent pipes to make sure there aren’t any puncture holes. Sometimes, your pipe can crack, so the air will go out of the heater without doing its purpose.

Also, chances are your vent pipes aren’t connected properly. This can also lead to supply problems.

All Rinnai water heaters come with an instruction manual that can let you know how everything’s supposed to look. Also, this will allow you to check all the clearance materials. Some models require you to move other items away from the heater, as they can block the air supply.

Rodents, wasps, and birds can create nests that can block your venting. This happens more often than you might think, even in urban areas.

Not only will this prevent your heater from working properly but it is also a fire hazard. Water heaters can explode, and you should never risk this.

Cold Water Sandwich

Cold water sandwich is one of those Rinnai tankless water heater problems you can do nothing about. Let’s explain.

If one of your family members has just finished showering and you’re next, you might feel warm water at the beginning, just to be blasted with cold water before the water starts heating up. This isn’t the heater’s fault.

Once the first person has finished showering, some warm water remained in the pipes. The warm water you initially felt isn’t the water your heater has just warmed up, but rather the leftover water from the previous shower.

While annoying, this isn’t a true issue and it doesn’t mean your Rinnai water heater is failing. The only thing you can do is to avoid getting into the shower right after another family member and wait for the cold water to pass.

Read Also: Rinnai Tankless Water Heater with No Hot Water

Other Rinnai Error Codes

rheem water heater

When troubleshooting Rinnai tankless water heater problems, you might run into some other problems that we didn’t mention in detail. This is because they are fairly rare on most other models, but they might still happen.

Here are some other error codes you might see:

  • Error Code 02: No burner operation during freeze protection mode.
  • Error Code 03: Power interruption during bath fill.
  • Error Code 14: Thermal fuse problems.
  • Error Code 16: Over temperature warming.
  • Error Code 32: Outgoing water temperature sensor fault.
  • Error Code 33: Heat exchanger outgoing temperature sensor fault.
  • Error Code 34: Combustion air temperature sensor fault.
  • Error Code 52: Modulating solenoid valve signal abnormal.
  • Error Code 61: Combustion fan failure.
  • Error Code 65: Water flow control fault.
  • Error Code 71: Solenoid valve circuit fault.
  • Error Code 72: Flame sensing device fault.

Most of these problems will require help from a professional. Whether they are caused by a scale buildup or a system failure, it’s best not to deal with such problems on your own. Not only are you risking further damage, but you might even endanger yourself and your entire property.

Even if you don’t see any code but suspect your heater isn’t working properly, it’s a good idea to call a professional who can help.

Bottom Line

While rare, Rinnai tankless water heater problems can still occur. Every single type of water heater can experience issues from time to time and this doesn’t necessarily mean the product is bad.

Regularly flushing your water heater is generally the best thing you can do to prolong the life of your unit. Yearly maintenance is the key to a long-lasting unit.

When you know the error codes, troubleshooting these issues is much more straightforward than if you had no clue to what you’re doing. As such, always look at the screen, see if there is anything you can do, and don’t hesitate to call a professional plumber for help.