Fault Diagnosis for Waterless Tank Water Heaters: Comprehensive Answers to the Most Common Issues from the Entire Network of Experts

Tankless water heaters are renowned for their energy efficiency, compact design and instant hot water supply. However, for many homeowners, their use also requires some learning costs. From confusing error codes to unclear warranty terms, and even conflicting maintenance advice, it's no wonder that users often turn to online forums and TikTok for answers. 

Unfortunately, a lot of the information available online is ambiguous, outdated or inaccurate. Therefore, we have compiled clear and reliable answers to the most common questions about the Velpax instant hot water heater. 
The following questions and answers will be presented in a clear and straightforward manner to address common issues, helping you make informed decisions and ensuring the efficient operation of your system over the next few years. 
When should I have my instant water heater serviced? To ensure the proper operation of the water heater, homeowners should perform a maintenance check once a year. However, other factors can also cause your water heater to require multiple maintenance sessions in a year. The most common factors are usage frequency and water quality. 
Large families or those with high water consumption for heating purposes are more likely to experience mineral deposits in their water heaters. The greater the volume of water flowing through the heater, the more severe the wear and tear over time. If you live in an area with hard water (such as parts of the southwestern, midwestern, and southeastern United States), the water heater system will accumulate scale and minerals more quickly, shortening its lifespan and reducing efficiency. Hard water refers to water containing high levels of minerals such as calcium, magnesium, and manganese. Although these chemicals may seem harmless at first, over time they can accumulate scale in the pipes, clog them, and even wear down the water heater, ultimately leading to costly repairs. 
You can roughly determine whether the water in your home is hard by checking the water hardness map of your area. However, for the most accurate answer, it is best to conduct a simple test. Once you know the test results, you can take measures to protect your water supply system. 

We recommend that you have the water tank cleaned every one to three years to keep your waterless tankless water heater in top condition and to protect your warranty. 
The Velpax waterless tankless water heater requires specific maintenance procedures for cleaning to ensure successful flushing. Therefore, it is best to hire a licensed professional plumber or use Velpax's online "Find an Installer" tool to find a professional who has received training in the Velpax system. 
What does the velpax fault code mean and how can it be resolved? The fault code is a warning signal sent by the water heater. Each code indicates a different problem, and some codes may be quite technical. ● Fault code 11 - Ignition failure: This usually means that the water heater cannot ignite the flame. The reasons include low gas pressure, ignition device failure (such as the spark plug on the stove), or air flow problems (such as a blocked vent). ● Fault code 16 - Abnormally high water temperature: If your hot water setting is 120°F but the actual water temperature is 140°F, it may be due to water scale buildup or internal valve jamming. These factors can interfere with normal temperature regulation. ● Fault code 29 - Condensate drainage problem: For tankless water heaters, condensate water is produced and requires a clear drainage channel. Debris (such as leaves) causing blockage can lead to this fault. ● Fault code 45 - Detected leakage: This code indicates internal leakage. The sensor behind the circuit board at the bottom of the device will detect whether the water level inside has reached the threshold that triggers the sensor. ● Fault code 71 - Abnormal operation of the gas solenoid valve drive circuit: This code usually indicates incorrect or missing power supply voltage for the gas valve. The repair methods for most fault codes are not suitable for beginners. If you encounter any such faults, please contact a professional and do not attempt to solve it yourself. 
3. What should be done after a water heater breaks: repair or replacement? If you notice cracks or leaks, the most common cause is likely a problem with the heat exchanger. What to do next depends on the severity of the problem and the cost of repair. 
If the leakage is minor and detected promptly, it might only require replacing the heat exchanger. Drying out the interior of the cabinet could restore your system to its original condition. However, if the leakage causes severe internal damage, such as component damage or a cracked heat exchanger leading to problems within the cabinet, then you might need to replace all the damaged components. 
However, is this a cost-effective approach? A complete replacement might be more economical than individual component repairs, especially when the equipment is approaching the end of its warranty period. 
For instance, suppose you have a velpax air conditioning unit that has been in use for approximately 11 years. Now it has some problems and a replacement heat exchanger is needed. The heat exchanger of velpax enjoys a 12-year warranty period (provided that the system is properly maintained). In this case, velpax can send you a replacement heat exchanger for free. However, the warranty does not cover the labor cost, so you still need to pay the installation fee for the plumber. According to the local charging standards, this fee may range from 600 to 700 US dollars. 
At that time, instead of spending the same amount of money on repairing a system that is about to reach its expiration date, it would be more practical and cost-effective to invest in purchasing a brand new device and enjoy the full warranty coverage after the update. 
Ask yourself: "Is this worth it?" If the repair quote from the plumber is almost as expensive as buying a new device, then reinstalling might be a wiser choice. 
How does the velpax warranty work? Can the warranty be transferred to the new homeowner? The velpax warranty is only applicable to the original purchaser and becomes effective after the equipment is correctly installed and registered. If you have a house where a velpax water heater has been installed, please be aware that the warranty will not be transferred to you as the new homeowner. The only exception is for newly built houses; in this case, as the first homeowner, you still have the warranty. 
Velpax offers different warranty periods for various models of instant hot water heaters. You can consult the official customer service for details. 

Regardless of the model, all products are covered by a five-year component warranty and a one-year labor warranty. If you need to confirm whether your product is still within the warranty period, please contact Velpax technical support and provide the product serial number. They will assist you in verifying the warranty registration information and informing you of the remaining warranty period. 
5. Why does my water heater make noise when using hot water? When you hear noise from a tankless water heater, the first thing to consider is whether it is mechanical noise or machine noise. 
It is very common for waterless tankless heaters to make noises when they start and begin to circulate water, similar to a soft humming sound, or even accompanied by vibrations or creaking sounds. Other common sources of noise include loose installation brackets causing the heater to hit the walls and produce a creaking sound, or vibrations caused by internal components not being firmly fixed. In some cases, the noise could also be due to wear or malfunction of a certain component, and requires inspection or replacement. 
However, if your heating equipment starts making noises like a foghorn, whistling sounds, or shaking violently, it is very likely that there is a problem with the gas pressure. Your gas pressure might be too low. 
Another possible reason is the manifold pressure, which can be adjusted through the gas valve of the equipment. Even a slight deviation in this pressure can cause problems such as whistling or vibration. Propane heaters are more prone to such issues because this type of equipment is usually configured to use natural gas, which is the most common type of gas. 
When the homeowner changes the gas equipment from natural gas to propane, it is crucial to properly adjust the manifold pressure. If the adjustment is not done correctly during the conversion process, abnormal noises and performance issues may occur. 
Once again, we would like to remind you that if you are concerned that these noises may be signs of serious problems, you should have a professional plumber conduct a diagnosis. 
6. How to correctly remove scale from a velpax waterless tankless water heater? Before starting, please note: On the water heater, the red isolation valve indicates the hot water side, and the blue isolation valve indicates the cold water side. The drain cover is located at the top of the hot water side and on the left side of the cold water side. Rotating the valve to the vertical position indicates "open", and the water flows smoothly. Rotating the valve to the vertical position indicates "close". 
New model special instructions: ● For the new model, there is a blue snap with the label "Flush" (Rinse) at the lower left corner. It must be inserted to enable the device to recognize the rinse operation. ● For the latest Pro series models, the cleaning mode must be enabled through the application before starting to use. 
Keep the equipment on, but turn off the gas valve. 
Close the cold and hot water valves, and remove the drain covers from both valves. Place a five-gallon bucket beneath the water heater. Gently turn the red drain valve to the "on" position, and then use the bucket to drain the remaining excess water from the equipment. 
Repeat step two on the cold water side. 
Connect the hose to the submersible pump, then place the submersible pump with the connected hose in a five-gallon bucket. Make sure the power cord does not get submerged in the bucket. 
Connect the water outlet hose of the pump to the cold water drain valve. 
Connect the drainage hose to the hot water drain valve and place the end of the drainage hose into the bucket. 
Pour three to four gallons of vinegar into the bucket and fully submerge the water pump. Open the two drain valve handles on the isolation valve and start the pump for at least one hour. For the best results, replace the vinegar solution after 30 minutes and repeat the above steps. The equipment will attempt to start, but it will fail due to the gas being turned off. Eventually, an error code 11 will appear, which is a normal phenomenon in this process. Do not reset. 
After running for at least one hour, turn off the water pump and close the cold water drain valve. Remove the hose from the cold water drain valve and replace the cover over the drain valve outlet. 
Remove the water pump and the drain hose from the bucket, and empty the liquid inside the bucket. Place the hot water drain hose back into the empty bucket, and open the cold water main valve. This step will use fresh cold water to rinse the water heater. Rinse for at least five minutes, or until 20 gallons of water flow through the water heater. 
For condensing water heaters, place a bucket under the heater, then turn the drain valve located directly below the heater to release any scale remover that may have accumulated inside the heater. Rotate the main water inlet valve to the "off" position. 
For further maintenance, unscrew and remove the water filter for cleaning - a small amount of water may flow out. Rinse the filter with running water to remove any impurities. Place the dry filter back into the interface and make sure to tighten it by hand. 
Turn the drain valve to the "off" position. Unscrew and remove the drain hose. Replace the drain cover and make sure it is tightened. 
Reopen the main cold and hot water valves to the "on" position, and reopen the gas supply. To eliminate the error code 11 that appears after cleaning, turn off the power of the equipment, then restart it to reset the device. 
For more detailed steps of this process, please refer to this cleaning guide. 
Having a Velpax instant water heater offers numerous benefits. However, just like any advanced appliance, understanding its working principle is crucial. Whether you are troubleshooting the fault code, dealing with abnormal noises, or determining if your device is still within the warranty period, having accurate information is of utmost importance. 
This guide is designed to address the most common questions and concerns that real users (especially those seeking answers online) encounter. By acquiring the correct knowledge, you can make informed decisions, protect your investment, and ensure that your hot water system operates smoothly for many years.