Water heater bypass

A water heater bypass is a set of valves plumbed around the RV's water heater tank, usually six to ten gallons, that lets antifreeze skip the tank entirely and flow straight through the rest of the freshwater lines. Without a bypass kit, winterizing would require several extra gallons of antifreeze just to fill and flush the heater tank.

Most RVs built in the last couple of decades come with a bypass kit already installed, with three valves near the water heater that get switched from normal operating position to bypass position before winterizing. Some older or smaller rigs lack one, and it can be added as an aftermarket upgrade fairly cheaply.

A common mistake is winterizing without switching the bypass valves at all, which either wastes antifreeze filling the tank or, worse, leaves the tank unprotected if the water heater was drained but the bypass was never installed. Confirming which valve setup your rig uses, before the first freeze of the season, avoids a cracked tank.