Tankless water heaters are a popular choice for many homeowners due to their efficiency and ability to provide hot water on demand. However, like any system, they can experience issues that leave you without the hot water you need.
If you’re wondering, “Why isn’t my tankless water heater working?”—we’ve got you covered! Read on to explore some possible reasons you’re experiencing issues, and what you can do to solve them.
Power Supply Issue or Ignition Failure
Sometimes the issue is as simple as your water heater not having access to a proper power source. Likewise, if there is a fault in the electrical or gas connections, you may experience an ignition failure. This is when there isn’t enough fuel to ignite the initial flame that heats your water.
If you have an electric tankless water heater, check your main electrical panel to see if any breakers have been tripped. If you have a gas heater, make sure you still have open access—whether that’s through paying your utility bill or making sure your gas valve is open.
Mineral Buildup
Hard water deposits, minerals, and other sediment can build up in your heater, causing blockages and potential issues. While this happens less often with tankless water heaters than with traditional heaters, it can still be a problem that reduces your water heater’s efficiency and how much hot water is produced.
If you’re experiencing issues with buildup, contact a plumbing professional to properly flush your system and clear out any obstructions. Regular water heater maintenance can help reduce how often you need to flush out your entire system.
Outside Temperatures
If your tankless water heater is installed in an area exposed to cold weather, freezing temperatures could play a role in how well it functions. Many units come with freeze protection to prevent the water inside from freezing, but if this feature fails or the heater isn't properly insulated, freezing can occur and cause damage.
To avoid this, ensure your water heater is installed in a location where it’s shielded from extreme cold, and consider adding extra insulation around the unit for added protection. In the winter months, frozen pipes can also prevent hot water from flowing to your appliances. If this happens, carefully thaw your pipes using safe methods before attempting to get hot water again.
Minimum Flow Rate
One common reason your tankless water heater might not be working properly is if the minimum flow rate is not being met. Tankless water heaters require a certain amount of water flow to activate and heat the water. If the flow rate is too low, the unit may not turn on, leaving you with cold water.
Check the specifications for your particular unit or ask a plumbing professional to determine the required minimum flow rate, and ensure that your fixtures and plumbing are capable of meeting that demand. If needed, consider upgrading to higher flow fixtures or addressing any plumbing restrictions to get your hot water flowing again.
Overloaded System
Another reason your tankless water heater might not be delivering hot water is that you’re running too many appliances simultaneously. Tankless water heaters are designed to heat water on demand, but they can only heat so much water at a time. If multiple faucets, showers, or appliances (like the dishwasher and washing machine) are running at once, the demand for hot water can exceed the unit's capacity.
When this happens, the water temperature may drop, or you might experience lukewarm water instead of hot. To avoid this, try staggering the use of hot water appliances or consider upgrading to a larger unit that can handle higher flow rates.
Blocked Exhaust
Proper ventilation is essential for the efficient and safe operation of your tankless water heater. If your unit isn’t working, it could be due to a blocked exhaust system. This system needs a clear path to vent air outside while it’s in use.
To check for blockages, start by inspecting the exhaust pipe to ensure it's unobstructed. Make sure the vents both inside and outside your home are free of debris, and verify there are no holes or damage to the pipes. Additionally, double-check that the system was installed according to the manufacturer's guidelines—installing it too close to other objects can cause blockages or restricted airflow.
If the exhaust system is blocked or improperly set up, it can lead to overheating, shutdown, or inefficiency. Regularly inspect and clear your venting system to ensure your tankless water heater runs smoothly.
Cold or Hot Water Sandwich
If you've ever experienced a sudden burst of cold water in the middle of your shower, only to have the hot water return moments later, you’ve encountered the dreaded "cold water sandwich." This happens most often in households where people are taking back-to-back showers or running multiple appliances at once.
What happens is after the first shower, hot water remains in the pipes leading to the next person’s shower. As you step in, the first few moments of warmth are just the leftover hot water from the previous shower. But once that runs out, the cold water in the pipes takes over before your tankless water heater heats up fresh water for you. The result? A brief cold burst before the water temperature settles back to normal.
This issue occurs because tankless water heaters heat water on demand, and any cold water left in the pipes between the heater and your shower must pass through before the new heated water arrives. The further your shower is from the heater, the more noticeable this gap will be. While there's no way to fully prevent the cold water sandwich, you can avoid it by waiting a few moments after someone else finishes showering, allowing the cold water to clear the pipes before stepping in.
By understanding the factors that can affect the performance of your tankless water heater, you can troubleshoot issues and ensure your system operates efficiently. If you’ve gone over these common issues and are still asking “Why isn’t my tankless water heater working?”—it may be time to reach out to a plumbing professional for help.
At Ciriello Plumbing, we promise expertise, honesty, and efficiency to the homes and businesses we service in Greater Indianapolis, including Carmel, Fishers, & Greenwood. From residential plumbing repairs to commercial installations, our expert team is dedicated to providing exceptional craftsmanship and unparalleled customer service. For reliable plumbing services you can trust, contact Ciriello Plumbing Solutions today.
