RV Water Heater Not Heating? Diagnose the Gas Side and the Electric Side Separately

You pull into a site after a seven-hour day, everyone wants a shower, and the tap runs cold. Maybe the heater clicks a few times and gives up. Maybe it does nothing at all. Either way you're outside in the dark poking at an access door with a flashlight, and every forum thread says something different.

Here's what makes an RV water heater far easier to diagnose than people expect: almost every one of them is really two heaters sharing one tank. There's a propane burner with its own ignition system, and — on most rigs built in the last fifteen years — a 120-volt electric element that works like the one in a house water heater. They fail independently. Which one is dead tells you almost everything, and you can determine it in about ten minutes without a single tool.

Start here: figure out which half actually failed

Turn on both. Give the propane side ten minutes and the electric side a full hour — a 1,440-watt element takes roughly 60 to 70 minutes to bring a cold 6-gallon tank up to temperature, while the gas burner does it in about 20. Run the hot tap after each.

• Works on gas, not on electric — you have a burned-out element, a tripped breaker or GFCI, or a bad switch. The tank, the plumbing, and the thermostat are fine.
• Works on electric, not on gas — the fault is in the propane train: supply, the DSI board, the igniter, the gas valve, or the burner tube.
• Dead on both — suspect the thing they share. That's the ECO (Energy Cut Off) high-limit switch, the thermostat, or an empty tank. Do not start ordering parts until you've checked those three.
• Neither one, and no water pressure at the hot taps at all — your winterize bypass valves are closed. The heater is dry and doing nothing because there's nothing in it.

That last one deserves emphasis. The bypass valves behind the tank route water around the heater so you're not putting six gallons of antifreeze through it every fall. Leaving them bypassed after a spring de-winterize is the most common "my water heater died" call, and it isn't even a failure yet — but it becomes one the moment somebody flips the electric switch on an empty tank.

The electric side: element, ECO, and the dry-tank mistake

A dry-fired element is the number one killer. The element is designed to shed heat into water; with nothing but air around it, it cooks itself in seconds. Always confirm the tank is full — open a hot tap and run it until it flows steady with no sputtering — before energizing the electric side.

To test the element, kill the breaker, pull the outside access cover, and put a multimeter across its two terminals. A healthy 1,440-watt element reads roughly 8 to 10 ohms. Infinite resistance means it's open and needs replacing. Also check continuity from either terminal to the tank body: continuity there means the element has failed to ground, which is exactly what trips a GFCI or breaker every time you switch it on.

The ECO is a small disc switch clipped against the tank, wired in series with everything. It opens around 180°F and it does not reset itself on most models — there's a red button you press until it clicks. Before you reset it a second time, ask why it tripped. A recurring ECO trip usually means a thermostat that has stopped opening, a heavy lime scale layer holding heat against the sensor, or a tank that was run low. Resetting it over and over on a rig with a stuck thermostat is how you end up with scalding water at the tap.

The gas side: from the propane tank to the burner tube

Work outward from the supply, not inward from the heater.

1. Confirm propane is actually flowing. Light a stove burner. If the range won't hold a flame either, you have an empty bottle, a closed valve, a tripped excess-flow lockout in the tank valve (open the bottle slowly — a fast open trips it), or a failing two-stage regulator. A weak regulator that starves several appliances at once is a real pattern; if your absorption fridge is also struggling on gas, read our notes on diagnosing a fridge that won't cool alongside this, because the shared cause is often the regulator.
2. Check 12-volt battery voltage. Direct spark ignition boards need healthy DC. Below about 10.5 volts they'll click and lock out even with perfect propane. A heater that only misbehaves on battery and works on shore power is telling you about your batteries, not your heater.
3. Listen to the lockout pattern. Most DSI systems try three times, then fault. Clicking with no whoosh means spark but no gas — gas valve solenoid, or the ECO/thermostat circuit that feeds it. Whoosh with no sustained flame means the flame sensor isn't proving ignition, often just a sooted or misaligned electrode. The gap should be about 1/8 inch and sitting directly in the flame path.
4. Look up the burner tube with a flashlight. Mud dauber and spider nests in that tube are so common they're practically a maintenance item, especially on rigs that sat a season. The insects are drawn to the mercaptan odorant in propane. A blocked or partially blocked tube gives you a lazy yellow flame, sooting, and repeated lockouts. Compressed air and a bottle brush clear it.
5. Check the outside vent and the flue for wasp nests and road debris. A blocked flue can push exhaust back at the ECO and trip it.

Anything past this point — gas valve replacement, control board swap, leak testing a fitting you disturbed — is propane work. Do it with a soap solution and a manometer, or hand it to somebody who has both.

Hot water that runs out in two minutes

This is a different complaint with different causes, and it's worth separating because people replace perfectly good parts chasing it.

• A partially open bypass valve mixes cold straight into the hot line. You get warm-ish water that never gets hot and never lasts. Check the valve positions first, every time.
• Scale on the element or tank bottom cuts effective capacity and slows recovery. Suburban tanks are porcelain-lined steel and take a sacrificial anode rod; pull it annually and replace it once it's about 75 percent eaten. Atwood and Dometic tanks are aluminum-clad and use no anode rod at all — installing one in an Atwood is a common and pointless mistake.
• A six-gallon tank is a six-gallon tank. With a low-flow shower head and the burner running, that's realistically six to nine minutes of shower. Nothing is broken.
• A weeping T&P relief valve usually means the air gap at the top of the tank collapsed. Kill power and propane, shut the water off, open the relief lever, and drain a little to restore the pocket.

When to call a pro

Call when the ECO keeps tripping after a reset, when you have propane work beyond clearing a burner tube, when the tank is leaking from the seam or around the element threads, or when you see soot, yellow flame, or scorching around the vent. Sooting is a combustion problem, and combustion problems in a sealed sidewall next to where you sleep are not a learn-as-you-go project.

Also call before you buy a whole heater. A gas valve or a control board is a same-visit fix; a tank replacement is not, and the two get confused constantly. We connect owners with vetted, licensed, insured local techs — from RV water heater repair in Denver to Austin — and most of these faults are diagnosed at your site in under an hour.

FAQ

Can I run the propane and electric sides at the same time? On DE-model heaters, yes, and it roughly halves recovery time. Just never run the electric side unless you've confirmed the tank is full.

Why does my heater work at home but lock out at a campground? Usually battery voltage or altitude. A converter on shore power hides a weak battery bank; boondocking exposes it. High elevation can also cause intermittent lockouts on an already-marginal gas train.

How long should an RV water heater last? Ten to fifteen years is typical. Annual anode replacement on a steel Suburban tank and an annual tank flush both extend that considerably.

Is a rotten-egg smell in the hot water dangerous? Not dangerous, but it means sulfate bacteria are reacting with the anode rod. Flush the tank, replace the anode with an aluminum-zinc rod, and it usually clears.

If you've narrowed it down and don't want to spend your vacation on it, call 833-FIXED-RV (1-833-349-3378). One call, answered live by a real person 24/7, and we connect you to a vetted local pro who comes to your rig instead of you hauling it to a shop with a three-week backlog. Every job in our network carries a $2,500 Workmanship Guarantee. See every city and service we cover on the RV repair hub.