Picture this: it’s a cold winter morning and you’re getting ready for work. You jump into the shower, turn on the water, and wait for it to warm up. But as time passes, the water remains stubbornly cold. You check the faucet and realize that there’s no hot water coming out.

The culprit? Your Rinnai tankless water heater. Nothing is more frustrating than a lack of hot water, especially when you’re counting on it to start your day.

In this article, we’ll take a deep dive into the common causes of Rinnai tankless water heater no hot water issues and explore some solutions to get your hot water flowing again. So, if you’re tired of cold showers and want to learn how to fix your Rinnai tankless water heater, keep reading.

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Understanding Rinnai Tankless Water Heaters

How they work

Rinnai tankless water heaters are a type of on-demand water heating system that heat the water as it circulates through the unit. When hot water is needed, cold water flows into the unit and is heated by a heat exchanger. The hot water is then delivered to the faucet or showerhead.

Unlike traditional tank-style water heaters, which store a large amount of heated water in a tank, tankless systems do not require any storage space. This means that they can be installed in smaller spaces and are ideal for homes with limited storage space.

Advantages over traditional water heaters

There are several advantages to using Rinnai tankless water heaters over traditional tank-style units. Firstly, they are more energy-efficient because they only heat the amount of hot water that is needed at any given time, rather than constantly heating an entire tank of hot water. This can result in significant energy savings over time.

Additionally, because there is no storage tank involved, there is no risk of running out of hot water during high-demand periods, such as when multiple people are taking showers simultaneously. Because Rinnai tankless systems have a much longer lifespan than traditional units (up to 20 years), homeowners can save money on replacement costs in the long run.

Common problems and solutions

Despite their many advantages, Rinnai tankless systems can experience problems from time to time. One common issue is lime scale buildup on the heat exchanger or other components within the unit. Lime scale buildup can reduce efficiency and even cause damage if left unchecked.

Regular maintenance and descaling can help prevent this issue. Another common problem is inadequate gas supply or pressure.

If your unit isn’t getting enough gas flow it will not function properly and you may experience a lack of hot water. In this case, it’s important to consult a professional plumber or gas technician to assess and fix the issue.

If your Rinnai tankless water heater is not producing hot water at all, it could be due to a malfunctioning temperature sensor or faulty heating element. Both of these components can be replaced by a trained technician in order to restore hot water production.

Reasons for No Hot Water with Rinnai Tankless Water Heaters and Some Quick Fixes.

Solution: Before you try any of our additional fixes try the manufacturer’s troubleshooting steps.

  1. Clean inlet water supply filter. Where the water comes into the unit there is a small screen filter just take this out and make sure it is squeaky clean.
  2. On new installations ensure hot and cold water lines are not reversed. I know it’s the obvious but lets not pretend we are incapable of making stupid mistakes.
  3. Check for bleed over. Isolate the unit from the home by turning off the hot water line to the dwelling. Isolate the circulating system also if you have one. Open your pressure relief valve; if the unit fires, there is bleed over in your plumbing. Bleed your plumbing lines and it should resolve the issue.
  4. Ensure you have at least the minimum flow rate required to fire the unit. If your water pressure is very low this could be the issue.
  5. Ensure the turbine spins freely. If it’s jammed the unit won’t heat water to protect itself
  6. Measure the resistance of the water flow control sensor.
  7. Remote control does not light up but you have 12 VDC at the terminals for controls. If you have a power issue that is more complicated than just the DC being unplugged you should probably get a pro to help.

If you try all 7 of these trouble shooting steps and you still haven’t found the issue try these next steps.

Insufficient gas supply

If this is your issue your most likely going to be showing error code 11 or maybe error code 12.

One of the most common reasons for a lack of hot water from a Rinnai tankless water heater is an insufficient gas supply. If there isn’t enough gas flowing to the unit, it won’t be able to heat the water properly. This could be caused by a variety of factors, such as low gas pressure in your home or a problem with the gas line leading to the unit.

To check whether this is the issue, you can turn on another appliance that uses gas, such as your oven or stove. If those appliances aren’t functioning properly either, then it’s likely that you have an issue with your home’s gas supply.

How to fix:
Check for any kinks or closed valves on your gas line near your hot water heater. If you have a pressure gauge near the supply to your unit make sure the unit has gas pressure and is within the manufacturer’s limits.

This is honestly not the most likely cause of you not getting any hot water out of your unit but if it is it’s probably going to be a general lack of gas to your home or water heater.

Dirty or clogged burner

If this is your issue your most likely going to have error code 10 or 11 but also possibly 12.

Why you might not be getting any hot water from your Rinnai tankless water heater is due to a dirty or clogged burner. Over time, mineral buildup and debris can accumulate on the burner and prevent it from functioning correctly.

When this happens, it won’t be able to heat up the water properly and may even shut off completely. Cleaning or replacing the burner is usually necessary in this case.

How to fix:

If your Rinnai tankless water heater is not producing hot water due to a dirty or clogged burner, cleaning it may help resolve this issue. Before attempting this, turn off power and shut off both cold and hot valves connected to the unit.

Use a soft-bristled brush like a toothbrush to remove any debris accumulated on top of it without applying too much force that can damage it. If cleaning doesn’t solve the problem, replacing your burner assembly may be necessary.

Malfunctioning temperature sensor

This is most likely going to be error code 16 but also could be 32, 33 or 34.

The temperature sensor in your Rinnai tankless water heater is responsible for monitoring and regulating the temperature of the hot water being produced by the unit. If there’s an issue with this sensor, then it may not be able to accurately detect what temperature it is heating the water to. This causes the unit to go into limp mode no hot water will produced at all. Problems with temperature sensors are often caused by exposure to extreme temperatures over time or damage due to mishandling during installation.

How to fix:

A faulty temperature sensor that incorrectly reads water temperatures and prevents heating activation altogether. To test this component, turn off power and shut off both valves again. Locate the temperature sensor (near incoming cold-water lines) behind its cover plate on your unit’s front panel with a multimeter set up in ohms mode.

Touch one probe each onto corresponding terminals; if you get zero ohms reading from them when tested together as well as individually against ground terminal, you can conclude it’s working properly. If not, replace the temperature sensor.

Faulty heating element

If none of these other issues seem to be causing a lack of hot water from your Rinnai tankless water heater, it could be a problem with the heating element itself. Over time, these elements can become worn or damaged and will need to be replaced in order for the unit to function properly. This does not normally trip an error code instead you just don’t have hot water. A professional technician can diagnose whether this is the issue and replace the heating element if necessary.

Final thoughts on troubleshooting no hot water issue with Rinnai tankless water heaters

In conclusion, if you’re experiencing the frustration of a Rinnai tankless water heater not producing hot water, take a deep breath and don’t panic. By following the simple troubleshooting steps outlined in this article, you can quickly and easily resolve this common issue.

Armed with a better understanding of your unit and its potential pitfalls, you can confidently troubleshoot any future problems that may arise.

Remember, regular maintenance is key to keeping your Rinnai tankless heater running smoothly for years to come, so be sure to follow the manufacturer’s recommended maintenance schedule. And if you’re ever unsure about any aspect of maintaining or repairing your unit, don’t hesitate to call in a professional for assistance.

With a little know-how and some TLC, your Rinnai tankless water heater will provide you with reliable hot water whenever you need it.

Rinnai FAQ
Our own troubleshooting guide Rinnai tankless water heater error codes