RV Water Heater Bypass - How to Install and Use It

Without a bypass, winterizing your camper means pumping 6-10 gallons of antifreeze through the water heater tank. That’s wasteful and expensive. A bypass kit routes antifreeze around the tank instead of through it.

How the Bypass Works

The bypass kit adds valves to the hot and cold water lines going into the water heater. Three valve positions control water flow:

Normal mode: Water flows through the heater. Both inlet/outlet valves open, bypass valve closed.

Bypass mode: Water flows around the heater. Both inlet/outlet valves closed, bypass valve open.

Types of Bypass Kits

Single-Valve Bypass

One valve on a crossover line between hot and cold pipes. Simplest setup but allows some backflow through the tank.

Two-Valve Bypass

Valves on both the inlet and outlet lines, plus a crossover. Better isolation but no bypass-specific valve.

Three-Valve Bypass (Recommended)

A valve on the inlet, outlet and crossover line. Complete isolation of the water heater. Most factory installations use this setup.

Checking If You Already Have One

Look behind the water heater access panel (exterior of the RV). You’ll see the hot and cold water lines connecting to the back of the heater. If there are valves on these lines with a crossover pipe between them, you have a bypass.

Most RVs built after 2005 have one factory-installed.

Installation Steps

Tools Needed

• Adjustable wrench
• Teflon tape
• Bypass kit (match your pipe size — usually 1/2” PEX or copper)
• SharkBite fittings or PEX crimp rings (depending on your plumbing type)

Process

1. Turn off the water heater and let it cool
2. Shut off the water supply (pump off, city water disconnected)
3. Drain the water heater through the drain plug
4. Access the back of the water heater (exterior panel)
5. Cut the hot and cold lines about 6 inches from the heater connections
6. Install the bypass valves following the kit instructions
7. Connect the crossover line between hot and cold
8. Apply Teflon tape to all threaded connections
9. Test for leaks with water pressure — check every joint

PEX vs Copper

If your RV uses PEX (flexible plastic tubing), use SharkBite push-fit fittings for the easiest installation. No special tools needed — just push the fitting onto the pipe until it clicks.

For copper plumbing, use compression fittings or solder. Compression is easier for DIY and doesn’t require a torch near the RV’s walls.

Using the Bypass

Winterizing (Bypass Mode)

1. Close both heater valves (inlet and outlet)
2. Open the bypass valve (crossover)
3. Drain the water heater
4. Antifreeze now flows around the heater through the bypass line

Normal Use

1. Open both heater valves (inlet and outlet)
2. Close the bypass valve (crossover)
3. Fill the water heater (open a hot faucet until water flows steadily)
4. Then turn the heater on

Never turn on the water heater with the tank empty. Running a dry tank burns out the heating element (electric) or damages the tank (gas).

Common Mistakes

Forgetting to switch back to normal mode in spring. You’ll have cold water only and wonder why the heater isn’t working. Check valve positions before every trip.

Not draining the heater before bypass. The standing water in the tank can freeze and damage it even though the lines are bypassed. Always drain the tank.

Over-tightening fittings. PEX fittings crack when over-tightened. Hand-tight plus a quarter turn with a wrench is enough.

Related Articles

• How to Winterize a Camper
• RV Water Pump Not Working
• RV Black Tank Flush Guide