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Installing a Tankless Water Heater on a Well Water System


WARNING! Keep in mind that well pumps are 220 volt. The combination of water, metallic surfaces and electricity can be very dangerous if not understood and/or respected to the utmost level of safety. Well water pump systems have all three of these components and are complicated devices. There is substantial risk of electrical shock and/or serious injury. 

NEVER work on a well pump switch without disconnecting the power supply.


It is ALWAYS BEST to ask a professional to make these adjustments for you.


The Problem:

The most common question we receive from tankless water heater users on well water systems is fluctuating temperature when using their hot water. This is usually in an eight to ten degree temperature range which is most noticeable when taking a shower. After many hours of research and testing in our Indiana facility with an actual well water system, the EZ Tankless technical team believes that they have solved this common problem for most persons using a tankless water heater on a well and pump water delivery system.

The Causes and the components explained:

If you are using a well water system, you more than likely have an electric well pump. This pump has a low end ("ON" switch) and high end ("OFF" switch). The average home owner will usually have a 30psi/50psi or 40psi/60psi well pump switch. This switch works in unison with your pressure tank.

An explanation of the operation of the pressure tank. Most older systems have a small pressure tank and most newer systems have a much larger tank. What this tank does is to regulate the water pressure during the cycles of the well pump. Inside the tank is a large rubber diaphragm which presses against the water in the lower portion of the tank to achieve a more consistent water pressure supply for the user. This is not an exact science and the pressure tank has a limited ability to control pressure at a precise level. Newer large pressure-tank systems are more effective but the vast majority of well users have older systems. Above the centrally located flexible rubber diaphragm is compressed air which gives the diaphragm its force that applies the downward pressure to the water in the lower half of the tank. (Typically there is a small bicycle type schrader valve on the top of the tank for checking the air pressure and refilling as necessary.) If the pressure tank is in good condition, the water in the lower half never comes into contact with the air in the top half. As it is "just there" and has no electrical connection or electric switches, this tank will last a very long time. Consequently, this is usually the most neglected component in any older well system. As these tanks age, the diaphragm can fail or the air pressure may not be correct. Most homeowners never think to check the air supply above the diaphragm, or to inspect the tank until a problem arises.

Additional notes: Typically there is a large information sticker on the pressure tank itself. On this sticker will be the tank size, model information, and the correct air pressure requirement. Use a bicycle tire gauge to check this pressure. Be aware that too much pressure can cause the diaphragm to fail or even cause the tank to burst. Especially if is is old and corroded. An old tank may also have corrosion and sediment inside, so occasionally replacing this item is not a bad idea and should be considered. If you are switching to a tankless water heater, it is a good idea to address every component in your well system at that time. This is a good opportunity to bring the system up to date. Place a new larger pressure tank into the system, have the pump and switch professionally serviced, and enjoy the improvements.

An explanation of the operation of the well pump pressure switch. When you open a faucet or turn on the shower on a well system, your water pressure immediately begins to drop and continues to drop until it hits the low-end setting on your pump motor switch, then the pump kicks-on and rapidly brings the pressure back up until it hits the high-end on your switch and the pump turns-off. (If you connect a water pressure gauge to your water line you can easily see this fluctuation. The rise in pressure is rapid and depends upon the GPM capacity of the pump itself, and the fall in water pressure depends upon the amount of water flowing from an open faucet or shower head.)

Even when the pressure tank is operating correctly there can be a constant fluctuation of pressure as the pump cycles. This pressure change due to the pump cycling is the reason for the fluctuation in temperature you are experiencing with your tankless water heater.

Why does a modern tankless heater have this fluctuation? The reason that this is happening is simple. No matter what brand of tankless heater, modern ones with temperature controlled hot water use sensors and switches to regulate the burner and fan motor to supply consistent hot water at your desired pre-set temperature. This works well when the tankless heater is connected to a water supply with consistent pressure. (Typical municipal systems have a constant 45 to 65 psi delivered to the home.) When the system is subjected to rapidly rising and falling pressure, the tankless heater is trying to supply the selected hot water temperature, but in reality it is "chasing" the constantly changing pressure. As the pressure rapidly rises when the well pump starts, the heater control system senses this and turns-up the burner to compensate. No sooner than the heater adjusts itself to this rising pressure, the pump turns-off and the pressure begins to fall until the pump turns on again and the cycle repeats itself. The heater never catches up to the pressure changes because the water pressure never stops changing. This racing to keep up with this constantly changing pressure is why the temperature is fluctuating.


You can do a combination of two relatively simple things.

  1. You can purchase a water pressure regulator. A water pressure regulator will keep the water at a constant pressure, thus eliminating the temperature fluctuation.
  2. Increase the low-end setting on your pump switch to decrease the range of pressure fluctuation.

Using a water pressure regulator as the solution. In our tests in our Indiana facility, we reduced an eight to ten degree temperature fluctuation to one to two degrees with this simple installation of a pressure regulator and no modification of the pump switch settings.

Pump settings explained. You will want the low-end setting of your pump switch to be slightly less than or equal to the setting on the water pressure regulator, this will keep your water pressure at a consistent level. Simply place the regulator in-line on the inlet (cold side) of the water system near the entry point to the home. (Or at what point you wish to regulate your hot and cold mixture for reasons of comfort) You may wish to mount the regulator near the tankless heater.

For example, if your pump has a 40/60 switch (40psi is the low-side of the pressure). Set the regulator to 40 psi and there will be a constant supply of 40 psi water going into the water system and the tankless heater. Or change the switch to 50/60 range and then set the regulator at 50psi etc... Keep in mind that when the pump switch range is adjusted in this way, the pump will run in shorter cycles. With this "regulator" solution, the heater will no longer be chasing after a constantly changing pressure and will supply a consistent temperature.

IMPORTANT NOTE about locating the regulator and its use: Please realize that if you are only regulating the water going directly into the tankless heater, the cold side of your shower will still have a well pump related pressure fluctuation. In this scenario, you may actually correct the problem of the heater "chasing" the pressure changes but continue to have a shower temperature "comfort related" temperature fluctuation due to the cold side variations. This is caused by your "mix" or blend of hot and cold changing on the cold side via pressure fluctuation caused by the well pump switch cycles. This is the reason we recommend that both the cold and hot sides of the shower pass through the regulator. This way your pressure fluctuations are regulated equally on both sides. Giving you a consistent blend of hot and cold which results in a more comfortable shower.


REFLECTING ON A CHANGING WORLD: Remember, this is not the fault of the intelligent design of modern tankless water heaters, it is related to the fact that they are designed and built for the large portion of the worlds population that have a supply of water delivered to the home under a consistent level of pressure. Even some towns have varying pressure depending upon the time of day and how many residents are using the central system. But, these systems are so large that pressure fluctuation happens at a very slow pace. A change that the heater can easily manage. Well systems with rapid pressure changes are the only scenario that is difficult for a modern tankless "smart" heater to manage and control. With an antiquated large holding tank-type water heater, the heater did not respond to flow and pressure changes as it simply heated that big tank of water at a very slow pace. Day in and day out, it ran to keep that big tank hot for the moment when the homeowner needed water. Kind of the same thing as keeping the car running in the driveway in case it was needed and we all know that is not the thing to do. The reason the temperature did not fluctuate with the old tank type system was because as the well-pump turned on and off, the pressure fluctuated equally on both the hot and cold sides. Therefore making the temperature constant. As the world becomes more energy efficient we all need to make some changes. This is really no different than switching from a large car with a large engine to a small car. We know that there is not as much room inside the smaller car and it typically has less power of the engine. The "economy" of the small car is a trade-off for the size and power of a larger car. As we know, there is a trade of some kind for energy savings. A carburetor for more complicated fuel injection for example. The primary reasons that people switch to smaller cars is to reduce the operating costs of driving and to save energy. Once the pressure of the well system is controlled the tankless water heater will operate as designed and deliver a consistent temperature of water within it's GPM specified parameters as well as saving energy thereby reducing utility costs.

NOTES: These tips are for professional use only, we accept no responsibility for those who try to work on their systems themselves. It is ALWAYS BEST to ask a professional to make these adjustments for you.


-- The EZ Tankless Team