How to Prevent Your Tankless Water Heater from Overheating

Many homeowners are concerned about their tankless water heaters freezing during the winter months, and rightly so. One of the most common problems associated with tankless water heaters is a frozen water supply.

One common issue that is often ignored involves overheating. If the tankless water heater is used for a prolonged period, then it can build up enough heat within the unit that cause it to be damaged as well.

There is also the issue of having your hot water being too hot. That concern will be addressed with the overheating issue as well.

Here are the steps you’ll want to take to ensure your tankless water heater is performing as it should.

Step 1: Check your thermostat settings

Some of the models we have reviewed may not look like they are equipped with an adjustable thermostat from the outside, but it is there. Entry-level models may have a dial or gauge that must be turned to set the thermostat to the correct temperature. This dial or gauge may be located inside the housing of the unit, without an exterior control.

Many tankless water heaters have a digital thermostat display that will tell you the exact temperature of your water. Mid-range units will likely have a dial on the exterior of the unit which allows you to control the temperature.

Because many tankless water heaters are mounted to the exterior of the home, the thermostat can be inadvertently moved, creating the overheating issue. If your hot water is too hot or your water heater case seems hot to the touch, double-check the thermostat settings. Make an adjustment if necessary.

Most tankless water heaters operate best at a temperature of 120F or less.

Step 2: Check for mechanical faults

There are two common mechanical issues which occur with tankless water heaters that can cause an overheating issue. The thermostat may have a mechanical fault in it or the heating elements of the unit may have a mechanical fault.

Impacts can cause these mechanical issues. The most common reason for a thermostat or heating element to malfunction, however, is scale buildup.

When too much scale is contained within the tankless water heater, it must work harder to heat the water to the temperature you desire. With enough scale in place, the unit overheats because it cannot heat the water to the temperature set at the thermostat.

The easiest way to prevent this issue is to regularly clean your tankless water heater. Regularly inspecting the unit to ensure it has not received any impact damage will also help to prevent overheating issues from ruining your investment.

Step 3: Inspect the pressure and temperature valves

If the first two steps don’t seem to be impacting the performance of your tankless water heater, but you still have an overheating issue, then there is a good chance that you have a malfunctioning valve.

Valves which do not supply enough water, or do not allow enough water to escape from the unit, can cause the water heater to begin overheating.

Open the exterior housing of your unit and look for obvious faults or defects. If the valves have been moved somehow, they will not be completely parallel or perpendicular, depending upon how they were installed. Move them into the correct position and this should remove the overheating issue.

If they are positioned correctly, try closing the valve. You should be able to hear the system adjust to the change. Should nothing happen, then you may need to replace the valve to correct the issue.

Some valves may appear to be operating correctly, while having small leaks which impact performance. These leaks may be difficult to detect. If everything looks like it is performing as it should, place some soapy water around the fittings of the valves. If you see bubbles that grow, then you’ll have discovered a leak which must be corrected to reduce the overheating issue.

What If I Cannot Find the Cause for My Overheating Issue?

Some overheating issues can remain a mystery, even after a thorough inspection. If you encounter such an issue, it is a good idea to contact the customer service number from your manufacturer, especially if your tankless water heater is new. There may be something covered by your warranty that can correct this issue.

If your unit is outside the warranty period, then contact a plumber who is familiar with tankless systems for support.

An overheating tankless water heater can damage your home and cause personal injuries. With regular inspections and the occasional cleaning, many issues with overheating can be completely prevented.

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Greg Mattson

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