Rheem Tankless Water Heater No Hot Water [Why+ How To Fix]

Rheem Tankless water heater no hot water is frustrating in the case of both gas and electric models. The common reasons for both models include:

• Too low-temperature setting
• Not enough water demand or flow rate is too high
• Water piping is frozen
• Using too hot water fixture at a time 
• Wrong adjustment of the anti-scald valve in the shower handle

To get the maximum temperature, rotate the temperature higher and adjust the water pressure to the required level. Figure out the frozen pipe and thaw it to unfreeze. Ensure the anti-scald valve in your shower handles on the hotter side.  In case the system is overloaded, turn off the extra hot water fixture.

If the problem still persists, you need to visually inspect your gas or electric model and find out the actual reasons. Let’s explore all the reasons and effective solutions through this comprehensive guide!

Common Reasons For Rheem Tankless Water Heater No Hot Water [5 Easy Solutions]

I’ve been using a Rheem tankless model for many years. From that experience, I’ve identified some specific reasons that are responsible for Rheem tankless water heater not getting hot enough. 

Don’t worry! No matter whether you’re using a Rheem gas or electrically operated model, I’m here with you till the end with all the easiest but highly effective solutions I’ve personally applied to resolve my heater’s heating issues. 

Let’s dive straight into the key topics.

01. Water Temperature Is Too Low

If your Rheem tankless water heater is not getting enough, first and foremost check the temperature setting on your unit. The best chances are the temperature at the remote control is set too low which is why you are not getting water as your expected hot level. 

If that is so, check and increase the temperature to the maximum level to let the water hot enough.

How To Fix:

At the remote controller, you’ll get 120 -Degrees F as a default setting which you can upgrade to 140 degrees F. 

Most of the time, the temperature setting on the controller gets locked and you need to disable it to adjust the temperature. For instance:

• Press down the up arrow button.
• Keep holding it until the temperature flashes 140 degrees F. 
• When it flashes, hit the down arrow button while holding the up arrow. You may hear a beep sound
• Now set your desired temperature and press the Enter button to store the setting.

02. Incorrect Water Flow

If the temp is all okay, I bet the next suspected factor behind your Rheem tankless water heater not getting hot enough is the incorrect water flow rate to the unit. Don’t worry, I am here with you to guide how to ensure correct water flow to your unit.

 For both gas and electric tankless water heaters, a minimum water flow is required to run the heater and produce hot water efficiently. 

Here you have to learn two factors. First, if the water flow rate is too low, it’ll bypass the heater’s minimum flow rate and ultimately the burner won’t ignite.   

On the contrary, the flow rate should not be so high. If that is so, it will run through more water into the unit and get it out before getting hot.  

So in short you have to ensure the water flow rate to your tankless unit is at recommended level (Go through the manual to learn that!). No worries! We’re here for you to solve the issue.

How To Fix:

First off, take a water pressure regulator and measure the flow rate to your unit. If it’s not at the recommended level, adjust it as followings:

1. Check The Water Shut-off Valve 

Inspect the water shut-off valve from the bottom of the unit. You will get two valves here labeled red and blue colored handles. Check the cold shut-off valve and open it all the way. Turning the valve lever counterclockwise will let the water flow thoroughly.

2.  Open The Hot Water Faucet

Regarding the insufficient water pressure, chances are the hot water faucets remain closed. Thus check the hot water faucets and open them all the way. Otherwise, the burner won’t ignite. 

Most of the time, users find the faucets are open but still, no water coming from them. For instance, clogged fixture aerators are another culprit to blame. Without any hassling, simply disassemble the faucet parts and clean it out with any sharp object. Check out the debris and obstruction in the water pipe as well and clean it. 

3. Adjust The High Water Pressure

In case, the water pressure is too high, you can easily minimize it by installing a flow regulator or flow restrictor in the water lines.

03. Frozen Pipes

When I had been dealing with the Rheem tankless water heater not heating issues, I drove depth and was totally surprised that my plumbing system got frozen, leading to the issue. Yes! you heard it right! 

In fact in your case nas well, if you are using your tankless unit in cold weather and it is chilly outside, the best chance is that the pipes or water lines of your water heater get frozen. Ultimately you’re not getting hot water from our hot water faucet at your demanded temperature level. 

But the fact that needs to come to your knowledge is every Rheem tankless water heater unit is equipped with a Freeze Protection feature that prevents the heater from freezing to an ambient temperature. 

Most of the time, the freeze protection features fail when there is too much cold outside. Anyway, there is a quick and effective tip to protect the piping system from freezing and to use the heater in such chilly weather. 

Let’s explore that! 

How To Fix:

To unfreeze your tankless unit, you need to figure out the frozen pipe of the system and then need to thaw it. Here is the step-by-step process to do so:

Step #1: First off, unscrew the front cover, and set it aside. 

Step #2: In the interior and exterior plumbing system of your Rheem tankless water heater. 

Step #3: Figure out the frozen pipes from the inside and outside of the system. 

Step #4: Now, open one of the hot water faucets it’s crucial as the water needs to flow through after thawing.

Step #5: Then, take a hairdryer and start putting heat to the frozen pipe area to thaw it. Keep it moving and don’t put much heat in one place as it may cause damage. 

Step #6: Keep going until the hot water starts flowing for the fixtures. You can use heat tape and insulation to prevent future freeze events.

04. Mixing Too Much Cold Water 

Most of the time, the problem related to no hot water in Rheem tankless water heater lies in the plumbing system. The best chances are you are mixing too much cold water with your water heater which is preventing the water from heating properly.  

If that is so, the anti-scald valve or mixing valve in the shower handle is the only culprit to blame(If you have one!) 

The anti-scald valve is the safety device in the shower handle that is designed to mix hot and cold water to ensure outcome water at a comfortable temperature.

In case, it is not adjusted properly or goes bad, you won;y get water at your preferred temperature.

How To Fix:

As a fix, you need to disassemble the shower handle and adjust the mixing valve properly. Here is how to do it:

Step #1: First off, take an Allen wrench and remove the screws of the shower handle. Take out the shower handle and expose the hot water valve stem.

Step #2: When done, remove the knob from the stem and you will see an O-ring at the center part. Take it out of the connection.

Step #3: Now, pull the valve stem slightly out and start turning it to the hotter side. It might be counterclockwise. 

Step #4: When done, set back the knob and O-ring back onto the stem. Reinstall the shower handle and check whether you are getting hot water now or not!

If not, no need to get hassle! We have many more solutions for you!

05. System Overload

After doing all the above steps and still, the scenario, step back and check how many fixtures you are running for your heater. If you are running too many hot water fixtures, it will overload the system and that is one of the major reasons for not producing hot water as it should.

Let me clear it up! 

Every tankless water heater has a minimum flow rate capacity that determines how much hot water can be used simultaneously. If you choose much more hot water activity, it will stretch your tankless water heater to its limit. When this happens, your water heater may also shut down when you need warm water.

How To Fix:

As a fix, shut off all the extra taps, and better to run only one fixture until the hot water returns. If the problem persists continuously, you can install two or more tankless water heaters in parallel to fulfill the simultaneous demands of hot water. Otherwise, you need to upgrade your tankless unit with a higher flow rate capacity.

After doing all the above steps, we hope that you are getting hot water from your Rheem tankless water heater as before. If not, you need to go through a deeper inspection of your tankless unit and that will certainly differ for both gas and electric models. 

Read on to learn how you will visually inspect your heater to solve the issue by yourself.  

Rheem Tankless Gas Water Heater No Hot Water

Well! All those above factors are the common reasons causing heating issues in your heater. Now from my real life experience, I’ll walk you through the remaining culprits in case your Rheem tankless water heater not getting hot enough problem along with their instant solutions:

i) Faulty Gas Supply

If you have a gas-operated Rheem tankless water heater and no hot water is coming out from it, a faulty gas supply is the root reason here. There are a few factors that might be responsible for a gas supply issue in your heater. Such as:

• Using incorrect gas type
• Gas shut-off valves are not opened all the way.
• Insufficient gas pressure
• Not enough gas in the LP tank or the gas supply is being cut off
• Obstruction in the gas supply line.

How To Fix:

Here is the complete checklist to fix the gas supply interruption in your Rheem tankless water heater:

First off ensure you are using the correct type of fuel for your heater unit. For instance, go through the manual to know whether your heater requires LP or natural gas.

When you are sure about that, it’s time to check out the LP tank to see whether there is sufficient fuel. If not refill it and purge the air after refilling. 

Now inspect the gas line for obstructions. Remove the obstruction to let the gas flow thoroughly to the unit. Then ensure the gas shut-off valve of your heater is opened all the way. 

Last but not least, measure the manifold gas pressure for your heater using a gas manometer. 

If it is not on the recommended level, calibrate and adjust the gas pressure following your manual. 

ii) Mixing Valve Malfunctions

The mixing valve is one of the major elements located underneath the Rheem tankless water heater that is designed to control the water temp by mixing cold water into it. 

In case the valve starts malfunctioning, it will fail to blend the hot and the cold water properly and as a result, you won’t get water from your heater unit at your required temperature level. 

Most of the time, you may notice drip or leaks from the mixing valve when it malfunctions or is damaged completely.

How To Fix:

In the troubleshooting step, you need to locate the mixing valve in your tankless water heater and verify whether it is in working condition or not. If you’re getting it hard to inspect the mixing valve, we would suggest hiring a professional for you to do the best task for you.

iii) Clogged Water Filter

If you’ve a gas-equipped water heater, the water filter at the bottom of your Rheem tankless water heater unit is quite known to you. 

It is the major part of the tankless water heater that features to protect the unit from mineral build-up and sediment and preserves the lifespan of the heater. In short, it is like scale inhibitors that prevent scale from accumulating in all of the orifices inside by sequestering hardness minerals in the solution.

As for always being in contact with hard water, clogging the filter screen with hard particles is quite obvious. And when this happens, water fails to flow through it and ultimately the unit doesn’t deliver enough hot water. As for the solution, you need to clean it.

Vi) How To Clean Water Filter In Rheem Tankless Water Filter?

Here are the simple steps to clean out the water filter in your Rheem unit:

Step #1: First off, turn off your water heater from the remote controller. Then turn off the water shut-off valve to your water heater.

Step #2: When done, it’s time to drain your water heater. And then, locate the water filter from the base of the cold water inlet line as shown in the above picture.

Step #3: Gently unscrew it and take it out. While doing so, make sure you have a bucket in your hand as the water will come out while removing the filter.

Step #4: Take a brush and scrub the filter screen to remove the stuck hard particles from it. You can use a Q-tip or toothpick for better cleaning and then wash it with running water.

Step #5: When the cleaning is done, install it back in place and screw it tightly.

v) Scale Buildup In The Heat Exchanger

Over time, unlike other tankless water heater models, Rheem tankless water heater accumulates minerals from the hard water during the heating process. It is the most common phenomenon and known term among tankless water heater users. 

Basically, the mineral sediment from the calcium and magnesium accumulates onto the internal surfaces of a heat exchanger. Heat exchangers are extremely vulnerable to limescale buildup and due to that, it loses their efficiency. 

As a result, it can’t transfer enough heat to the water. In the deeper case, the scale reduces the heater’s lifespan as well. As a solution, you will need to remove the scale build-up to restore the heater.  

How To Fix:

Flushing out the tankless water heater is the only effective way to get rid of all the limescale buildup from the heater inside. It successfully cleans up the hard particles from the heat exchanger fins and lets it back into normal operation. 

Now the question is how you will flush your Rheem tankless water heater. For instance, you can follow our comprehensive guide. Here we’ve guided the easiest processes to flush out the heater.

vi) Error Code Displayed On The Remote Control

If still,  Rheem gas tankless water heater not getting hot enough, chances are you have an error code on the remote controller. While operating the system, most of the time users encounter several error codes on the controller, indicating any specific issues in the system. When this appears, the complete heating process gets stalled and shut off the unit completely. 

How To Fix:

Look at the remote controller to find whether there is any error code on the display. Now, go through the “Service Error Code Chart” on the manual or Rheem’s website to figure out the meaning and fixing procedures. 

For instance, you can consult with a professional, or better you can take a look at the detailed Rheem error code troubleshooting guide where we’ll get all the error codes, meanings, and effective solution procedures.

Rheem Electric Tankless Water Heater No Hot Water

Here are the two main responsive factors to check and resolve to fix the no hot water issue in your Rheem electric tankless water heater: 

i) Degradation In Power Supply

If you’ve an electrically operated Rheem tankless water heater and no hot water is coming out from the system, interruption in the power supply is one of the leading reasons to blame.  As the tankless unit is electrically operated, it requires a fluent power supply to run smoothly. 

Keep note that, the heating elements of your tankless water heater are designed for 240 volts. With the lower voltage, the heating element won’t activate and fails to provide enough heating power.

Other major reasons for faulty power supply include:

• Incorrect wiring
• Defective circuit breaker
• The unit is not turned on properly
• Connected the heater to a non-functional electrical outlet.

How To Fix:

First of all, check and ensure you’ve conjected your water heater into a well-functional electrical outlet. If needed, test it by connecting any other appliance here. Also, it is essential to test the voltage supply of the outlet using a voltage meter.

Then, head to the circuit breaker and ensure it is in the “ON” position. In the case of a fuse, replace the blown fuse.

When done, it’s time to figure out the faulty wiring connection to the heater. Higher chances are you’ve installed your tankless unit recently and the wirings aren’t connected properly. Thus it’s better to check it out again. For instance, we would recommend contacting a professional to resolve the electric issues.

ii) Bad Heating Elements

Unlike other electric tankless water heater models, Rheem electric tankless water heater equips two robust copper immersion heating elements. The heating elements are designed to convert the electrical energy passing through it into heat and that is how it heats the water.

But in case, there are malfunctions in the heating elements and stop working, it won’t heat the water as before. So if you are dealing with your Rheem electric tankless water heater not getting hot enough issue, a bad heating element is the next susceptive factor that you need to concentrate on. 

How To Fix:

Turn off your tankless water heater and unplug it from the power connection. When done, unscrew the front panel and set it aside. Now inspect the heating elements to see whether it is in perfect working condition. 

For instance, you need to test the continuity of the heating element. If the result shows negative, be sure the heater element has burnt itself out completely. You won’t get hot water until the element is replaced. Contact a professional for further replacement discussion.  

Reach Out Rheem Technical Support 

If all the above troubleshooting steps fail to resolve your heating issues, be sure it is time to seek help from Rheem customer support. They will better understand the problems of your water heater and help you diagnose and potentially resolve the issue. 

Even if your Rheem product is still under warranty, they guide you through the warranty claim process. But when contacting Rheem technical support, you may ask for the following information:

• The model and serial number of your Rheem water heater.
• The product purchase date for warranty-related inquiries.
• The details of your location, including your address or the installation address. 
• Details of the persisting problem and any previous history when you’ve tried to fix this problem by a service included with dates

Essential Maintenance Tips To Follow To Prevent No Hot Water Issue In Your Rheem Tankless Water Heater?

If you want to prevent heating issues from your Rheem tankless model, here we have some pro tips for you. Just go through as in the provided suggestion and ensure your tankless model operates in tip-top condition:

Step-01: Periodically Flush Your Water Heater

It is essential to descale and flush your water heater at least once or better twice a year. it is even more important for you if you are living in a hard water area where hard water runs through your tankless system every time. Thus you need to flush your water heater to remove dirt, debris, or hard mineral buildup in the heater inside. 

Step-02: Check & Adjust The Water Flow

Regularly check and ensure that there is adequate water flow through the heater. In case the flow rate is too low, your water won’t activate. For instance, check for any blockages or restrictions in the water lines or adjust the water pressure regulator.

Step-03: Inspect The Water & Air Filters

Inspect and clean the heater air and water filters at least once a month and increase the efficiency of the element. The water filter restricts any large debris entering your water heater coming out of the water supply. 

Besides, the air filter helps to screen out impurities from the water before it’s heated. Thus cleaning these two essential elements is a must! 

To learn about the detailed procedures, you can head over to our comprehensive guide on Rheem tankless water heater maintenance.

FAQs:

In Closing!

If you’re experiencing Rheem tankless water heater no hot water issues, adjusting the water pressure and setting the temperature higher is enough to resolve the problem at most times. But in case not, you need to figure out the actual reasons for your tankless model.

If it is a gas model, make sure the gas shut-off valve is open and the unit has sufficient gas pressure. Track down the malfunctioning part like a clogged water filter or mixing valve and fix those. If you’ve an error code in the remote display, don’t ignore it as it might stall the complete heating process.

Anyway, if you’ve an electric model, first off, ensure the proper voltage supply to your unit. Also, inspect the heating element and test it to verify whether it is in well working order. 

Well! Here we’ve all for you! Hope our guide is well-proven enough to reach the exact troubleshoots! In case you’ll encounter any further issues, you can go through our comprehensive Rheem troubleshooting guide for better assistance.