How To Troubleshoot Common Problems With A Tankless Water Heater

July 14, 2023


Tankless water heaters have gained a lot of popularity in recent years due to their energy efficiency, longer lifespan, and cost savings. However, like any other appliance, they may experience problems from time to time. The good news is that most issues can be easily resolved with some troubleshooting techniques and by calling a professional HVAC contractor. In this blog, we will discuss how to troubleshoot common problems with a tankless water heater.

No Hot Water

One of the most common issues with a tankless water heater is the lack of hot water. If you are experiencing this problem, the first thing you should check is the powesr supply. Make sure that the unit is plugged in and that the circuit breaker is not tripped. If everything looks fine, then the problem could be with the water flow rate.

Tankless water heaters require a specific flow rate to work correctly. If the flow rate is too low, the unit may not heat the water sufficiently. You can increase the water flow rate by turning on multiple hot water taps at once. Alternatively, you can clean the inlet filter if it’s dirty, which can impede water flow.

Another potential cause of no hot water is a malfunctioning heating element. If the heating element is not working correctly, it may not be able to heat the water to the desired temperature.

Your tankless water heater may not produce hot water due to sediment buildup. Over time, sediment or debris can accumulate in the system and cause damage, including reducing the efficiency of the heating element. This can lead to a decrease in the temperature of the hot water or no hot water at all.

Fluctuating Water Temperature

If the water temperature fluctuates while you’re using hot water, it could be due to a clogged inlet filter or a an outlet blockage. A dirty filter can restrict water flow, causing the unit to struggle to maintain the desired water temperature. You can clean the inlet filter and flush the heat exchanger to fix this problem.

Additionally, if the unit is not adequately sized for your household’s hot water demand, it may struggle to keep up with the water temperature, causing fluctuations. To address fluctuating water temperature, it’s recommended to have a professional plumber inspect the tankless water heater to determine the root cause of the problem. They may recommend solutions such as descaling the system to remove sediment buildup, increasing the flow rate, adjusting the temperature setting, or replacing the unit if it’s not sized correctly.

Ignition Failure

Ignition failure is another common problem with tankless water heaters. If you notice that the unit is not turning on or producing hot water, it could be due to a lack of ignition. The first step in troubleshooting this problem is to check the gas supply. Make sure that the gas valve is on and the gas line is not obstructed.

If the gas supply is fine, then the problem may be with the igniter. You can inspect the igniter and clean it if it’s dirty. A dirty igniter may not produce enough heat to ignite the gas. If the igniter is damaged, you may need to replace it.

To address ignition failure in a tankless water heater, it’s recommended to have a professional plumber inspect the unit to determine the root cause of the problem. They may recommend solutions such as cleaning the burners, replacing the ignition component, fixing venting issues, or checking the gas supply.

Mineral Buildup

Hard water can cause mineral buildup in the heat exchanger, which can affect the unit’s efficiency and lifespan. Mineral buildup can cause problems such as fluctuating water temperature, reduced water flow, and even system failure. You can prevent mineral buildup by installing a water softener, flushing the system regularly, or by using a descaling agent.

If you suspect that mineral buildup is affecting your unit’s performance, you can inspect the heat exchanger and flush it to remove any buildup. You may need to repeat the process regularly if your water supply is particularly hard.


Tankless water heaters produce condensation when they operate. However, if you notice excessive condensation, it could be a sign of a problem. Excessive condensation can indicate that the unit is not venting properly.

Check the venting system to ensure that it’s not blocked or obstructed. If the venting system is fine, then the problem could be with the unit’s installation. Improper installation can cause condensation to accumulate inside the unit, leading to performance issues. If you suspect that the unit was not installed correctly, you should contact a professional to inspect it.

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