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RV Water Heater Thermostat Troubleshooting = No Cold Showers!

RV Water Heater Thermostat Troubleshooting = No Cold Showers!

An RV water heater thermostat is a surprisingly easy and inexpensive part to replace. But if you don’t have hot water in your RV, how do you know if a failed thermostat is the source of your problem? With parts ranging from circuit boards, gas valves, burner tubes, and more, how do you zero in on the problem? Could it just be as easy as hitting the reset button?

In this post, we’re focusing on RV water heater thermostat troubleshooting. We’ll cover how they work, the signs of a failing thermostat, and how to test yours to see if it’s the problem.

A water heater is a key piece of RV gear. Without it, you’ll be taking cold showers and washing dishes in cold water. If it stops working properly while you’re on a camping trip, knowing some common RV water heater troubleshooting tips, including how to test and replace the thermostat, could make a world of difference.

Here’s a step-by-step guide to troubleshooting an RV water heater thermostat, including a link to our post on exactly how to replace it if necessary.

How Does an RV Water Heater Thermostat Work?

A thermostat on an RV water heater is a simple device that’s normally “closed.” That means the electric switch is engaged to allow power to pass through. When the water in the heater’s tank reaches a set point (typically around 130°F / 54°C), the thermostat switch opens, breaking the circuit and causing the unit to stop heating water.

When the water temperature cools, or the hot water heater’s supply is mostly used up and replaced by the inflow of cooler water from the freshwater tank or city water supply, the thermostat closes the circuit. This triggers the water heater element to start heating water again. And so on.

There’s also a part called the E.C.O. (“Emergency Cut Off”), which is set to a higher temperature (usually about 180°F / 82°C). This acts as a backup in case the thermostat fails, which could allow the water to continue heating to dangerously high temperatures. It’s basically like a second thermostat, set to a higher temperature, to prevent the heating element from getting out of control.

Some RV water heaters have a single combined thermostat/E.C.O. unit. Suburban gas-electric water heaters have two. One is for the 12V DC propane side, and the other is for the 120V AC heating element that’s used when hooked up to shore or generator power.

Either way, the parts are inexpensive and easy to find.

Suburban 12V DC

SUBURBAN MFG 232282 Suburban T-STAT/Limit 12V
  • Product Type: Auto Accessory
  • Package Quantity: 1

Suburban 120V AC

Dometic/Atwood

Sale
ECO Thermostat Assembly Replacement for Atwood 91447 Replacement Part for Water Heater Repair Parts Fit for RV, Motor Home Emergency Cutoff Service Kit
  • 1.Water heater repair parts for RV, Motor, Home,etc.
  • 2.Fits Models:GCH6-4E, GCH6-6E, GCH6-7E, GC6A-7E, GH6-6E, GH6-7E, GH6-8E, G6A-6E, G6A-7E, G6A-8E, GCH6A-7E, GCH6A-8E, GCG6A-9E, GC6AA-7E, GC6AA-8E,...

What Are the Symptoms of RV Water Heater Thermostat Failure?

Signs of an RV water heater thermostat failure can be any of the following:

No Hot Water

In this case, the thermostat is likely to have failed in the “open” position, preventing the heater from ever firing up to heat the water. This can happen on 120V AC electric or 12V DC propane operation, depending on how your water heater is configured.

Water That’s Too Hot

If the water is too hot, the thermostat isn’t cutting off soon enough, allowing the water to continue heating past the set point. Or it isn’t cutting off at all, allowing the water to reach the E.C.O. set point before shutting off.

Intermittent Temperature Issues

Here the symptom is that the water temperature is sometimes okay but is either too hot or not hot enough at other times.

This was the problem we experienced with the Suburban water heater (those are the ones that use anode rods) in our Mountain Aire and may be quite common. That’s because, as we mentioned above, our model uses two thermostats. So if one fails and one doesn’t, the heater may still work… sometimes.

Like most RVers, we run our water heater on propane while boondocking. When plugged into shore power, or running our generator, we use 120V AC power to heat water.

Since only one of our Suburban water heater’s thermostats was failing (which is probably a typical scenario), it worked fine on propane, but not on 120V AC.

How to Test an RV Water Heater Thermostat

When the water heater is cool, you can test the thermostat(s) to ensure that you get continuity across the two terminals of either the 12V (propane use) or the 120V (shore/generator use) thermostats.

Testing involves using a multimeter to see if the thermostat is opening and closing its circuit at the correct temperatures.

This is the model we use:

Uni-T RMS Multimeter

Uni-T UT204 Auto-Ranging AC DC Ture RMS Auto/Manual Range Digital Handheld Clamp Meter Multimeter Test Tool
  • Measures both ac & dc current up to 400 amps, ideal for vehicles, rvs, marine boats & etc
  • Ac/dc voltage, current, resistance, frequency, continuity, duty cycle & diode check

Here’s a less expensive model that should work fine for most purposes:

AstroAI Multimeter

Sale
AstroAI Multimeter Tester 2000 Counts Digital Multimeter with DC AC Voltmeter and Ohm Volt Amp Meter ; Measures Voltage, Current, Resistance; Tests Live Wire, Continuity
  • VERSATILE DIGITAL MULTIMETER - Accurately measures AC/DC Voltage, DC Current, Resistance, and Diode. This Multimeter is a really useful tool for...
  • TROUBLESHOOTING WITH ACCURACY - This Multimeter has a sampling speed of 2 times per second; Built-in a backlight LCD display with 3 ½ digits (1999...

Remove the Access Cover

When the water heater is cool, remove the thermostat’s access cover. With our Suburban unit, this was simple to do by removing two screws using a flat-blade screwdriver.

Check for Continuity

Use your multimeter to check for continuity across the terminals of the thermostat. Check your multimeter owner’s manual for how to set it to the correct mode, as it can vary based on which model you have.

You’re looking to see whether or not there’s a continuous electrical connection allowing power to flow from one side to the other. Here’s a video showing you how to use a typical multimeter to test for continuity:

Determine Whether You Have a Faulty Thermostat

If the thermostat has failed in the “open” position, (preventing the heater from firing up at all), there will not be continuity across the thermostat when it’s cool (below the 130°F cutoff where it should be open). Of course, this test has to be done when the water is cool since it should be open when the water is hot.

If you try heating water, and it gets up above about 130F, your thermostat may have failed in the closed position, preventing the water heater from shutting off. If you check the water temperature as it’s being heated (we show how we do that in our video below) and see it climbing above 130, check your thermostat with the multi-meter.

If you continue to see continuity, the thermostat isn’t opening, so it’s not shutting off the heater. If it allows the temperature to get all the way up to about 180F before shutting the heat off, and the thermostat still shows continuity, you can be confident that the E.C.O. did its job, and your thermostat needs to be replaced, since it didn’t.

Replace A Faulty Thermostat

If your RV water heater thermostat has failed, you’ll need to replace it. Luckily, this is one of the cheapest, quickest, easiest DIY projects any RVer can do. No trip to an RV service center should be needed.

For a step-by-step guide, see our post on how to replace an RV water heater thermostat. Or just watch our short step-by-step video tutorial showing how we replaced our own water heater thermostat:

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Marc Goldstone

Wednesday 6th of March 2024

The metal dome thermostats have excessive hysteresis which causes the water temperature to vary by 10 degrees F or more from where the thermostat turns the heater off and where it comes back on. I for one prefer to set the water heater to 105 degrees F and use only the hot water valve when showering. This 10 degree variation is objectionable. Given the thermal mass of between 6 to 10 gallons of water a thermostat with much less hysteresis would be desirable. There is a solid state Integrated Circuit "TC622" which has only a 2 degree C hysteresis. (~4 degrees F) This TO220 package has a mounting tab that can be inserted between the water heater's tank and the steel chassis. A drop of heat sink compound optimizes the heat transfer. The high temperature sensor used on my Attwood water heater 180 degree F appears to only shut down the gas solenoid leaving only the low temperature thermostat to control the electric heating element. If the main temperature thermostat fails it can leave the electric element on and the only indication will be that the pressure/temperature relief valve will start to drip water.

When the parts arrive I will prototype this improved thermostat which will require splicing into the power and ground wires at teh controller board.

Marc Goldstone

Wednesday 28th of February 2024

I upgraded the original fixed threshold thermostat with an adjustable one. Though it works as advertized it should be noted that there is no way to adjust the hysteresis between the ON and OFF tempertatures. As such depending on how long it has been since the heating element was enabled the water temperature can drop resulting is luke warm but not hot water. I for one woudl like a thermostat that allows for setting the On and OFF temperatures to reduce the amount of hysteresis. This woudl provide a more constant water temperature at the cost of the heater cycling ON/OFF more frequently.

Marc Goldstone

Wednesday 6th of March 2024

@TheRVgeeks, I will share the results of testing the prototype thermostat with you. Packaging the circuitry will be the chalenge. I suppose that potting compound will protect the circuitry and that a small aluminum disc that the water heater's metal tabs will hold against the tank, with a screw to hold the IC's heat tab in contact with the aluminum disc. The IC will need to be powered by either the electric element or the gas power control signals. (dual diodes) Due to being retired I have no desire to manufacture and sell such a product but partnering with someone with that expertise might be of interest.

TheRVgeeks

Wednesday 28th of February 2024

We hear you, Marc. Would be nice to be able to control both the upper limit (how hot the water gets) and the LOWER limit (at what, lower, temperature a new heating cycle was begun). But we'd bet it could have something to do with the durability of the other components... and whether or not they NEED that amount of time to cool down enough no to be damaged by another heating cycle.

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