How to Bypass Water Heater in an RV?

If you are winterizing your RV and someone told you to bypass the water heater, they were not exaggerating. Filling a six or ten-gallon tank with antifreeze wastes product and does nothing to protect the tank itself. The bypass system isolates the heater so antifreeze flows only through the plumbing lines where protection is actually needed.

Most mistakes happen because valves are set incorrectly or the heater was not drained fully before switching modes. The process is simple once you understand the plumbing path, but the order matters.

How to Bypass the Water Heater in an RV (Step-by-Step)

This applies to standard tank-style heaters such as Suburban or Atwood units. Tankless RV water heaters usually do not require a traditional bypass because they do not store standing water in a tank.

Turn Off Power and Relieve Pressure

Shut off propane and electric modes before touching anything. If the electric element is left on while the tank is empty, it can burn out quickly. Turn off the water pump and disconnect the city water.

Open a hot faucet inside the RV to relieve pressure. Never remove a drain plug or anode rod from a pressurised or hot tank.

Drain the Water Heater Tank Completely

Remove the exterior access panel. On Suburban heaters, remove the anode rod. On Atwood models, remove the drain plug. Allow the tank to empty fully.

Lift the pressure relief valve briefly to speed draining and release trapped water. If sediment appears, that is normal. A rinse wand helps flush buildup before storage.

Bypassing without draining first traps water inside the tank, which defeats the purpose of winter protection.

Locate the RV Water Heater Bypass Valves

Most bypass valves sit on the backside of the heater, typically under a bed platform, behind a removable panel, or inside a cabinet. You will see PEX lines attached to the cold inlet and hot outlet.

A three-valve system has a valve on the cold line, a valve on the hot line, and a centre crossover valve. A two-valve system usually relies on a built-in check valve to prevent backflow.

If you do not see a crossover line, your RV may not have a bypass installed.

Set the Valves to Bypass Mode

On a three-valve system:

• Close the cold inlet valve.
• Close the hot outlet valve.
• Open the centre crossover valve.

This prevents water from entering the heater tank and redirects it across the bypass line.

On a two-valve system, rotate both valves so water is routed across the crossover and not into the tank. The exact orientation depends on how the manufacturer installed the valves, so follow the plumbing path visually.

Check out how to prevent rv pipes from freezing.

Confirm the Heater Is Fully Isolated

Turn the pump on briefly. Open a hot faucet.

If water flows immediately without the heater filling, the bypass is working. If you hear the tank filling or see water entering the heater, one of the valves is not positioned correctly, or the outlet check valve has failed.

Confirm isolation before pumping antifreeze into the system.

How RV Water Heater Bypass Systems Actually Work

The bypass system redirects water around the tank using a crossover line that connects the cold supply to the hot distribution line. In normal mode, water enters the tank, heats, and then exits through the hot outlet. In bypass mode, the tank is removed from the loop entirely.

Three-valve systems give you manual control over inlet and outlet flow. Two-valve systems rely on a check valve to block reverse flow into the tank. When that check valve sticks open or fails, water can backfeed into the tank even when the inlet valve is closed.

Understanding this flow path prevents misdiagnosing a plumbing issue as a valve-position mistake.

Suburban vs Atwood Differences That Matter

Suburban heaters use a steel tank and require an anode rod. That rod protects the tank from corrosion and must be removed for draining. Atwood heaters use an aluminium tank and a nylon drain plug instead.

Suburban models commonly include a check valve on the hot outlet. If you bypass the heater but the tank still fills, that check valve is often the cause. Replacing it restores proper isolation.

The bypass steps are the same for both brands, but the hardware differs enough that owners should confirm which model they have before draining.

Why Bypassing the Water Heater Is Necessary

When winterising, antifreeze is pumped through the plumbing lines. If the heater is not bypassed, antifreeze fills the tank first. That can require several additional gallons and still leaves risk if the water was not fully drained.

Bypassing saves antifreeze, speeds up winterisation, and prevents unnecessary chemical exposure inside the tank. It also isolates the heater if you are replacing it or troubleshooting pressure issues.

Common Problems After Bypassing

If you switch back to normal mode and get no hot water, check that both the inlet and outlet valves are open and the crossover valve is closed. One valve left in the wrong position blocks flow.

If the heater fills while in bypass mode, inspect the outlet check valve. A failed check valve allows water to enter the tank even when bypassed.

If air spits from faucets after returning to normal mode, that is typically the tank refilling and pushing air out of the lines.

If you accidentally power the heater while it is empty, inspect the electric element before reuse. Dry firing can damage it quickly.

Also check out how to sanitize fresh water tank in an RV.

What If Your RV Does Not Have a Bypass Installed

Some older units do not include a bypass kit. In that case, antifreeze will enter the heater unless you manually install one.

A bypass kit adds a crossover line and valve assembly between the cold inlet and hot outlet. Installation involves cutting into the PEX lines and adding fittings. It is a practical upgrade that reduces antifreeze use every winter.