Tankless water heaters, also known as on-demand water heaters, provide incredible efficiency and an endless supply of hot water when functioning correctly. By heating water directly as it flows through the unit rather than storing it in a large tank, these systems save space and reduce energy costs. However, because they are complex pieces of equipment with advanced internal components, they require specialized knowledge when problems arise.
At Newark Water Heater Pros, our technicians are extensively trained in tankless water heater repair. Whether your unit is failing to ignite, producing lukewarm water, showing an error code, or shutting off unexpectedly, we have the tools and expertise to accurately diagnose and resolve the issue quickly and safely. We understand how disruptive a lack of hot water can be, which is why we prioritize prompt, reliable service for homes and businesses throughout Newark, DE.
Common Tankless Water Heater Problems
While highly reliable, tankless water heaters can experience specific issues unique to their on-demand design. Because they utilize intricate computer boards, sensors, and high-efficiency heat exchangers, repairing them is often more complex than fixing a traditional storage tank heater. Some of the most common issues we encounter include failing to heat water to the set temperature, system lockouts triggered by safety sensors, restricted water flow, and unusual noises like rumbling or screeching during operation.
Diagnosing these problems requires understanding the interconnected systems within the unit: the gas or electric supply, the water flow sensors, the venting system, and the electronic controls. Our technicians perform comprehensive diagnostics to pinpoint the exact root cause, ensuring we replace only the necessary parts and restore your hot water efficiently.
Flow Rate Issues
One of the most frequent complaints with tankless water heaters is related to water flow. Tankless units operate based on flow rate, not just pressure. They are designed with a minimum flow activation threshold—typically between 0.4 and 0.5 gallons per minute (GPM). If a faucet is turned on but the flow is below this threshold (for instance, if a faucet has an aerator that severely restricts flow, or if you only turn the hot water tap on slightly), the unit's flow sensor will not recognize the demand, and the burner will not ignite.
Conversely, if multiple fixtures are running simultaneously (e.g., two showers and a washing machine), the demand might exceed the unit's maximum flow capacity. In this scenario, the heater will struggle to heat the water fast enough, resulting in lukewarm water or a significant drop in water pressure as the unit restricts flow to maintain the set temperature. We can help you determine if your flow issues are due to a malfunctioning flow sensor, a clogged inlet filter, or if the unit is simply undersized for your household's peak demand.
Temperature Fluctuations
Experiencing sudden changes in water temperature while showering is a common issue that often requires professional attention. One specific phenomenon associated with tankless heaters is the "cold water sandwich." If someone turns on the shower, turns it off to lather up, and then turns it back on, they might get hit with a blast of warm water, followed by a sudden burst of cold water, before it turns warm again. This happens because the unit takes a few seconds to reignite and heat the newly introduced cold water. The cold water that passed through during that delay creates the "sandwich."
While a cold water sandwich is somewhat inherent to older tankless designs (newer models often have small internal buffer tanks or recirculation pumps to mitigate this), persistent, unpredictable temperature fluctuations during continuous use indicate a problem. This could be caused by a faulty thermistor (temperature sensor), fluctuating gas pressure, or cross-connection plumbing issues where cold water is bleeding into the hot water line somewhere in the house.
Error Codes
Modern tankless water heaters are equipped with advanced diagnostic computer boards that monitor the system's performance. When a fault occurs, the unit will often shut down and display a flashing error code on its digital screen or remote controller. These codes are invaluable for troubleshooting, as they direct technicians straight to the problem area.
Different manufacturers (like Rinnai, Navien, Noritz, or Rheem) use different code systems. For example, a code might indicate an ignition failure, an exhaust blockage, a flame rod failure, or a dangerous temperature spike. While you can look up these codes in your owner's manual to understand the general issue, resolving them typically requires a professional. Attempting to bypass safety sensors or clear codes without fixing the underlying mechanical or electrical problem can lead to severe damage to the unit or create significant safety hazards involving gas leaks or carbon monoxide exposure.
Mineral Buildup and Scale
Hard water is the absolute worst enemy of a tankless water heater. As water is rapidly heated inside the unit's narrow heat exchanger, minerals like calcium and magnesium precipitate out of the water and cling to the metallic surfaces. Over time, this mineral scale acts as an insulator, forcing the burner to work harder and hotter to heat the water passing through. This not only dramatically reduces the unit's energy efficiency but also strains the heat exchanger.
If left unchecked, scale buildup can cause the heat exchanger to overheat and crack, leading to catastrophic failure and a very expensive repair or total replacement. In Newark and surrounding areas, hard water is common, making proactive scale management crucial. If you hear loud popping or rumbling noises coming from your tankless heater, or if the unit frequently displays an error code related to overheating, scale buildup is likely the culprit.
Maintenance for Tankless Units
To ensure longevity, efficiency, and uninterrupted service, tankless water heaters require regular, professional maintenance. The most critical aspect of this maintenance is an annual flush. During a flush, our technicians circulate a specialized descaling solution (typically food-grade white vinegar or a commercial descaler) through the heat exchanger for 45 to 60 minutes. This dissolves the mineral scale and restores the unit's heat transfer efficiency.
In addition to flushing the heat exchanger, comprehensive maintenance includes cleaning the in-line water filter to ensure proper flow, cleaning the combustion air fan and burner assembly to ensure proper ignition, and inspecting the venting system for any blockages or signs of corrosion. Regular maintenance not only prevents sudden breakdowns but is also typically required to keep the manufacturer's warranty valid.
Tankless Installation Considerations
If your current tankless water heater is beyond repair and requires replacement, or if you are considering upgrading from a traditional tank to a tankless system, there are several critical installation considerations. Proper installation is vital for a tankless unit to function safely and efficiently.
First, sizing is paramount. A unit must be sized based on your household's peak water demand (simultaneous fixtures running) and the groundwater temperature in Delaware. Second, gas lines often need to be upgraded; tankless heaters require a massive, instantaneous amount of gas (often over 199,000 BTUs) compared to standard tanks (around 40,000 BTUs), which may necessitate a larger diameter gas pipe. Third, venting requirements are strict. Most gas tankless heaters require specific Category III stainless steel or concentric PVC venting to handle the acidic condensation and high exhaust temperatures safely. Finally, they require a dedicated electrical outlet to power the computer board and sensors. Our team handles all these complex installation requirements with precision.
Tankless vs. Tank Replacement
When facing a major repair, homeowners often wonder if they should stick with a tankless unit or switch back to a standard storage tank. While the initial cost of a tankless replacement is higher than a tank replacement, the long-term benefits often outweigh the upfront investment. Tankless heaters offer significant energy savings by eliminating standby heat loss (the energy wasted keeping a large tank of water hot 24/7). They also have a longer expected lifespan—typically 15 to 20 years compared to 8 to 12 years for a tank heater—and they take up a fraction of the physical space.
However, if your home's gas supply cannot easily be upgraded, or if your budget strictly prohibits the higher installation cost, returning to a high-efficiency standard tank might be the practical choice. Our technicians provide honest, transparent assessments of your current system and offer options for both tankless repairs and various replacement types, helping you make the most informed decision for your home and budget.
Frequently Asked Questions
Why is my tankless water heater not producing hot water?
A lack of hot water from a tankless heater can be caused by the minimum flow rate not being met, a tripped breaker, a gas supply issue, scale buildup on the heat exchanger, or a dirty water filter. Checking for error codes on the unit's display can often provide a more specific diagnosis.
What does a cold water sandwich mean with a tankless heater?
A cold water sandwich occurs when you get a burst of hot water, followed by a gap of cold water, and then hot water again. This happens if you turn the hot water off and back on quickly. The heat exchanger takes a moment to reignite and heat the new water, causing a brief cold gap. Newer units often have internal buffers to reduce this effect.
How often does a tankless water heater need maintenance?
Tankless water heaters typically require annual maintenance, primarily descaling or flushing the heat exchanger. In areas with particularly hard water, like many parts of Delaware, you may need to flush it every 6 to 9 months to prevent mineral buildup and ensure optimal efficiency and longevity.
Why does my tankless water heater shut off during a shower?
If a tankless heater shuts off unexpectedly, it could be because multiple fixtures are being used and exceeding the unit's maximum flow capacity. It could also stem from improper venting, restricted airflow, a drop in gas pressure, or severe scale buildup restricting water flow through the heat exchanger causing it to overheat and trip a safety switch.
Is it worth repairing an older tankless water heater?
Tankless water heaters generally last 15-20 years. If your unit is under 12 years old, repair is often the best route, especially if the issue is a simple part replacement or needs a thorough flush. If the unit is over 15 years old and requiring a major repair, replacement may be more cost-effective.