Tankless water heaters are prized due to their low energy usage and operation costs, but that doesn't mean they are free of repair needs. Inconsistent water temperature is one complaint. Finding the cause is key to implementing the right repair.

1. Combined Use Issues

Although tankless heaters heat water on a continuous basis so they can't run out of hot water, they do have a limit on how many gallons they can heat per minute (GPM). If usage exceeds the GPM rate, then you will experience inconsistent heating. The cause is running hot water in multiple locations at once, such as showering while the hot water cycle is going on your washing machine. The fix is to install a heater with a higher GPM rating, install multiple heaters, or limit usage to one or two taps at a time.

2. Water Flow Restriction

Restriction in the flow of water can also impact heat consistency. Restrictions are often caused by mineral scale buildup in the supply lines or on the aerators and filters in the heater and along the line. A repair tech can clean out the scale and fix the issue. In some cases, the issue could be with a blocked inlet filter screen in the heater, which will require a replacement filter.

3. Low Flow Rate

A low flow rate can impact the consistency of the hot water that comes from the tap. Flow rate is controlled by the pressure regulating valves in the heater and along the water lines. There may also be a regulating valve in the affected tap. If the valve is failing or not set correctly, the flow rate is affected, and both water supply and heating consistency can be impacted. Repair or replacement of the valve is necessary.

4. Burner Malfunctions

Gas tankless water heaters may not deliver consistently if the burner malfunctions. Low or inconsistent water pressure can affect the burner, as the pilot light will only fire the burner when it detects a specific flow rate. Another issue is if there is a malfunction in the gas valve itself. If the pilot frequently goes out or the color flickers, it may need repair or a full replacement.

5. Mixing Valve Failure

The mixing valve combines the hot and cold water to give you a spectrum of warm temperatures dependent on the tap settings. If the mixing valve is stuck or failing, you may not be able to maintain consistently warm water — instead, it will drift back and forth to the hot or cold end of the spectrum. Replacement of the valve will fix the issue.

Contact a tankless water heater repair service for more help with inconsistent water temperature.