6 Common Tankless Water Heater Problems and How to Solve Them

by Eccotemp

Tankless water heaters are a great investment for your home or office. Not only are they highly efficient, but they can also save you money by heating water only on-demand. Although uncommon, issues can arise if something isn’t working correctly within your water heater.

Here are six of the most common problems and maintenance concerns for tankless water heaters:

  • Mineral Buildup
  • System Overload
  • Cold Water Sandwich
  • Air Supply or Exhaust Blockage
  • Ignition Failure
  • Flame Failure

Keep reading to learn what signs to look for when identifying these issues and how to fix them!

Problem 1: Mineral Buildup

Whether you use a traditional or a tankless water heater, you need to keep an eye out for mineral buildup inside your water heater. Hard water (in contrast with soft water) is water with a high mineral content, and the harder your water, the higher the potential for damaging mineral buildup. Calcium and Magnesium are the two minerals that most often cause scaly buildup, and this can impair the function of your water heater if you don't address is. To avoid damage, flush your water heater every six months with the Eccotemp EZ-Flush System Descaler Cleaning Kit. You can also use a water softener to slow the buildup.

Problem 2: System Overload

Depending on your tankless water heater's capacity, too many simultaneous hot water applications (such as multiple showers running) can overload your water heater. Your water heater may struggle to supply the hot water needed or shut down altogether if it becomes overloaded. If this happens, you should reduce the demand for hot water by limiting simultaneous applications, and you may want to consider resetting your unit. However, if your tankless water heater frequently becomes overloaded, you should consider either upgrading to a tankless water heater with a higher capacity or adding a second unit. Although a second unit might seem like a large investment, it can actually save you money in the long run since you’ll use less water while waiting for hot water to arrive and less gas to heat the water.

Problem 3: A Cold Water Sandwich

If your household frequently takes back-to-back showers, you may be familiar with the "cold water sandwich." Suppose a member of your household just finished showering and now it's your turn. You turn on the shower and feel warm water at first, but then get blasted with several seconds of cold water before the temperature slowly climbs back up. Here’s what happened: When the first shower ended, some hot water was remaining in the pipes on the way to the shower. When the second shower began, the initial warm water you felt was the trapped water. Although tankless water heaters are also called "instantaneous water heaters," they still take time to heat water, so after the trapped water was used up, you were left with a gap of unheated water. The further your water has to travel from the water heater to its destination, the more noticeable the gap. Unfortunately, there's no way to prevent this, but now that you're aware of the problem, you can avoid jumping in the shower until the cold water has passed. 

Problem 4. Your Air Supply or Exhaust is Blocked. 

For most tankless water heaters, the display with present an error code to inform you that your air supply or exhaust is blocked. This means your water heater is having issues with either combustion air or venting. First, inspect all vent pipes to ensure they are connected properly and free from puncture holes. Refer to your product manual to make sure the clearance requirements are being met, as installing your water heater too close to other objects can block the air supply and create a fire hazard. Birds nest, rodents and wasps nest can also block your venting, so be sure to thoroughly examine all vents that are located or lead outside your home.

Problem 5. Ignition Failure.

There are several reasons your water heater could fail to ignite. Often, this issue is caused by the gas supply, so check to make sure your propane tank is full before you do anything else. If your gas valve or water valves are not fully opened, this could also cause the ignition to fail. Check and open gas and water valves fully. If these steps do not resolve the ignition problem, then either your ignition pack has failed or there's a bigger problem. You should contact technical support to help you trouble shoot the issue and order replacement parts if necessary.

Problem 6. Flame Failure. 

Flame Failure is generally caused by either a gas pressure problem or an electrical issue. Just like ignition failure, you should first rule out simple causes such as a low propane tank or an unpaid gas bill. Other possible causes of flame failure include a gas line that’s too small, regulator failure, combustion issues, venting and more. Contact technical support for help with troubleshooting the issue further. 

Having a Tankless Water Heater Problem, But Unsure the Exact Problem?

Tankless water heaters are generally low maintenance and very efficient, but problems can still occur. This list includes some of the more common problems that people have with tankless hot water heaters, but it is not all inclusive.

If you don’t see the tankless water heater problem you’re having here, or if you need technical support with your water heater, please visit our help desk to schedule an appointment, or call us at 866-356-1992.


This article was originally published by Robinson's Plumbing Service and edited by Eccotemp.