Help solve temperature fluctuation on a tankless water heater

Troubleshoot temperature fluctuation problems

Learn how to troubleshoot and solve temperature fluctuation on a tankless water heater. You wouldn’t want to get caught in an unpleasant cold water sandwich situation when taking a shower. As the water temperature fluctuates delivered from a tankless water heater after the first few minutes you enjoy a nice hot shower and then changes to cold and back to warm/hot again.

Cold water sandwich 

This problematic issue especially on an electric tankless water heater occurs when the temperature variation when the heater is on as it provides hot water. When the water is not being dispensed from a fixture. Such as the tap being closed the unit shuts off, as the water inside the pipes get cooled. The water heater turns on and the cool water inside the pipes dispenses the cooled water before the hot water reaches the fixture. This results in cold water bursting or the cold water sandwich effect.

In homes it is suggested to set the water heater to a safe 120 degree temperature. One of the main reasons why temperature fluctuates is your tankless heater stopped working due to lack of low water. Usually the minimum flow rate is around 0.4-0.5. If your water heating system is not designed properly where the capacity is smaller than the demand, such as a change in flow from other fixtures in the home are opened or closed you can ‘feel the fluctuation of the temperature drop. Today, most tankless water heating systems have some type of water filtration or may have an inlet filter screen before water reaches the heater elements. It is suggested to change the filter or clean the inlet filter screen located at the bottom of the unit every six months or more frequently depending on your homes water usage.

Restriction of water flow

Water in Florida has a high mineral deposit count the can lead to a restriction of water flow in plumbing fixture parts such as long term mineral build up deposits on faucet aerators, shower heads. It would be a good idea to flush and clean each single one. You can soak them in household white vinegar to help dissolve the mineral deposits and flush the parts toughly with water before reinstalling.

Plumbing crossover

Temperature fluctuation may occur due to a plumbing crossover of a faulty mixing valve, incorrect plumbing, single lever faucet, or failed washer in a fixture. An easy way to find out is close the main line going to the heater and open a hot water tap, wait five minutes, and if water is still flowing there is a problem with a plumbing crossover.

Water pressure

A tankless water heater normally uses constant water pressure maintained at 30 psi. The pressure needs to be consistent so if you have a well on your property, be sure the pressure is present.

Mixing Valves

Do you have a mixing valve installed; a mixing valve lowers the temperature of hot water and mixes it with cold water. Check to see the water temperature on the valve.

Before any changes to fix your temperature fluctuation problem, measure the fill time to see what the proper activation flow rate is. If your experiencing longer than usual the odds is the activation rate is not met.

If you are experiencing difficulty to solve your temperature fluctuation problems and you need other home repairs, hire a professional handyman.