No hot water

[dawnmhurd]

Hot water working perfectly one day then on water at all. Checked heater, full of hot water. Opened all faucets and drained tank, but nothing. Any ideas?

[Kansas Gary]

Is the hot water bypass turned off by chance?

[Jackitup]

How are the valves on your hot water tank? Generally there are three one at the top on the red line one at the bottom on the blue line and one in the middle make sure you have the bypass one closed that is the one in the middle. What can happen is when the tank warms up there is pressure in the tank and when you open a tap the flow of water is forced out of the tank, when you turn the tap off the pressure in the tank is gone now what happens is the water will take the path of least resistance that is through the bypass hose the next time the tap is turned on.

[JRTJH]

Many (probably most) newer RV water heaters use a single valve bypass system. There is a 1/4 turn valve on the cold water inlet (bottom) and a one way outlet valve on the hot water exit (top) of the back of the water heater.

What is "supposed to happen" is with the valve in the "normal" position, water is routed into the water heater, gets hot, discharged through the top valve into the hot water plumbing. The one way outlet valve prevents backflow through the system and cold water is not circulated through the vertical bypass tube at the back of the water heater.

Sometimes that top valve will stick and prevent hot water from flowing through the water heater. Sometimes the bottom 1/4 turn valve will not seal properly and water "bypasses" the water heater.

If there is hot water in the water heater, I'd suspect that the top "exit valve" is stuck and the proper amount of hot water is not flowing through the tank. That valve is not repairable, but is replaceable. It's a plastic insert, screwed into a brass seat and is normally replaced as a unit. Here are photos of the 1/4 turn valve, the vertical bypass tube and the exit valve.

First, I'd turn the lower bypass valve "off" then turn it back "on" just to make sure it is properly working. Next, I'd feel the hot water plumbing about a foot or two from the top discharge valve to be sure hot water is flowing. If the PEX tubing is cold or only slightly warm, I'd suspect that the top discharge valve is stuck closed or partly closed and needs to be replaced.