Understanding RV Water Heater By-pass Systems

In this post I wanted to help RV owners learn everything you need to know about RV water heater by-pass systems.

Most RV manufactures today install water heater by-pass systems on the RVs they sell. The water heater by-pass system is used to separate the water heater from the RV’s plumbing system. The by-pass system can be used to drain the water heater, and to winterize the RV water system. When the by-pass system is used, it takes the cold water going to the water heater and routes it to the hot water plumbing line. When that happens the water heater is by-passed

Typically, you would use the by-pass system when the RV is winterized using an RV approved anti-freeze. When you bypass the water heater you can drain the water heater tank and the tank is safe for winter storage. By-passing the water heater saves you the cost of filling the water heater tank with six or more gallons of RV antifreeze to winterize the RV water system. For more information on winterizing your RV check out our RV winterizing and storing online training course.

How many types of RV water heater by-pass systems are there?

There are three common types of bypass systems, and you need to know which type you have. The types are 1, 2 & 3 manual valve operation.

On 1-valve systems the valve is located at cold water line and the by-pass line.

On two 2-valve systems, one valve is located at the cold-water inlet and the other valve is in the by-pass plumbing line.

On 3-valve systems, one valve is at the cold-water inlet, one is at the hot water outlet, and the third one is in the by-pass plumbing line.

The proper operation of each bypass system:

On a 1-valve system turn the valve at the cold-water supply line 90 degrees to the supply line. This stop the water supply to the water heater and open the by-pass line. Note: Some bypass valves use knobs rather than handles. In this case, just turn the knob until it is fully open or closed.

On a 2-valve system turn the valves located on the cold-water inlet and hot water outlet so the handle is in-line with the by-pass line. This will open the by-pass,  connecting the cold and hot water plumbing lines. Note: Some bypass valves use knobs rather than handles. Simply turn the knob until it is fully open or closed.

On a 3-valve system turn the manual valves located on the cold-water inlet and hot water outlet so the handle is in-line with the by-pass line just like the 2-valve system, then turn the manual valve in the by-pass line until the handle is in-line with the by-pass line. Note: some bypass valves use knobs rather than handles. Simply turn the knob until it is fully open or closed.

With the valves in these positions you can drain any water from the tank.

Caution: Never drain the tank when it is hot or under pressure. Open a hot water faucet to relieve pressure and allow the water to cool prior to draining.

To disengage the bypass system and allow water to enter the water heater, reverse the positions of the handles.

Symptoms of improperly positioned bypass valves are:

1. No hot water coming from the water heater.
2. You only get a short supply of hot water, which quickly turns lukewarm, and then cold.

If you experience these symptoms look to see if the by-pass valves are in the proper position.

When you de-winterize your RV, make sure your water heater tank is completely full of water prior to turning on the gas or electric systems on. A tank not full of water can damage the water heater controls. An easy way to check if the tank is full is to lift the lever on your temperature and pressure relief valve. If it is full, you will get water at the valve. Caution: Never open the T&P valve lever when the water heater is hot or under pressure.

For more information on RV water heater bypass systems watch this video we produced for Suburban water heaters. Top learn more about using and maintaining your RV visit our RV Online Training site.

Happy Camping,

Mark Polk
RV Education 101

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