Winterizing an RV Tankless Water Heater: Step-by-Step Guide (by Model)


If you’re a member of the RV tankless water heater club, congratulations! You now get to enjoy unlimited hot water on demand for showering, cooking, rinsing the dog, and drinking green tea. 

But what’s the protocol for winterizing an RV instant water heater? Contrary to what you’ve been told, there isn’t a one-size-fits-all answer. Some on-demand water heaters should be drained and left dry; others should be pumped full of liquid antifreeze. The Golden Rule is to check your Owner’s Manual!

However, for your convenience, I’ve compiled a list of common RV tankless water heaters with some instructions and tips on winterization. I’m not going to waste ink by copy-and-pasting the Owner’s Manual, so whenever possible, I’ll point you in that direction. 

Also, this post is about propane-powered tankless water heaters installed in RV sidewalls. I’ve never used or installed any of the “vent-free” indoor units, which are typically so small they can only be connected to a single fixture.  

>>> READ MORE: The New Kid on the Block: RV Tankless Water Heaters

Truma AquaGo Tankless Water Heater

The Truma AquaGo is the granddaddy of RV tankless water heaters. Sold by a German manufacturing company, the AquaGo boasts 60,000 BTUs of heating capacity and excellent temperature compensation. It’s one of the best instant water heaters on the market, although also perhaps the most expensive.

Truma AquaGo Comfort Plus tankless water heater installed in Class C sidewall

You should know that Truma guards its service department rather carefully. Most replacement parts are NOT available for retail sale. Even I, as an RV service technician, have to be approved under Truma to install and service their appliances. 

The AquaGo Base has no frost protection. However, the AquaGo Comfort and Comfort Plus models have “a built-in thermostat that will start the burner and the circulation pump whenever the temperature in the appliance falls below 41 degrees.” You can read the manual for more information, but unfortunately, the water heater can’t protect the rest of your plumbing system from freeze damage, so think of it as a safety measure. It’s not a free pass to use your RV in subfreezing conditions. 

The AquaGo also has its own cleaning process called “decalcification.” Other tankless water heaters just mumble something about keeping your water clean and maybe rinsing out with vinegar, but Truma actually gives you specific directions and a maintenance schedule. 

How to Winterize a Truma AquaGo Water Heater

Operating Manual

A Truma AquaGo water heater is supposed to be installed with a conventional bypass system, similar to a regular water heater. This was the responsibility of your RV manufacturer; hopefully they did it correctly! You can see the examples below:

Winterizing a Truma AquaGo is perhaps the easiest process of them all. All AquaGo’s (Base, Comfort, and Comfort Plus) have a yellow EZ Drain Lever that snaps into position. You can see it after you open the exterior access door. 

  1. Close the water heater bypass valve system.
  2. Open the EZ Drain Lever.
  3. Remove the water filter cartridge.
  4. Allow all water to drain.
  5. Close the EZ Drain Lever.
  6. (My recommendation) Let the water filter cartridge dry, and then store it in a Ziploc bag over the winter.

After that, you can continue with your nomal winterization, whether with antifreeze or compressed air. Point being, Truma wants you to bypass and drain their water heater; don’t pressurize it with compressed air or fill it up with antifreeze! 

Girard GSWH-2 Instant Water Heater

The Girard tankless water heater has been around a long time. The first generation isn’t sold anymore. It had the strange quirk where the user had to adjust the hot water temperature by adjusting its flow rate instead of just mixing and hot cold water.

The modern version, the GSWH-2, is a bit more intuitive. It now comes with a Control Panel that allows you to set the target temperature, and the GSWH-2 will do its best to self-adjust. 

Fun fact: You don’t quite get “endless” hot showers. As a safety measure, the Girard water heater will shut off after 20 minutes of continuous use and will display an En error code. You’ll have to reset the module to continue your sauna!

In my opinion, the downside to the Girard water heater is the minimum flow rate. It requires 0.9 Ga/min to operate, otherwise the burner will shut down. That’s quite high relative to competitors. Basically, you don’t have a slow “first gear;” the Girard won’t work if all you need is a trickle of water. 

Similar to the Truma, the Girard comes with basic freeze protection. As long as the unit is ON, it has 12V power, and sufficient propane supply, it will keep the heat exchanger above 38 degrees. However, this does not protect the rest of your plumbing system.

How to Winterize a Lippert Girard GSHW-2 Tankless Water Heater

Operation Manual

A Girard on-demand water heater does not require a factory water heater bypass system. “The very small amount of water present in the heat exchanger,” says Girard, “does not require the installation of a bypass kit.” 

Instead, Girard says to just leave the water heater in the system, and winterize using your preferred method of compressed air or liquid antifreeze. They don’t specify a maximum psi in their manual, but most other manufacturers limit pressure to 30 psi.

However, before you make assumptions about how your water heater is plumbed, I would take a peek at the back-end of your water heater and check out the plumbing. The installer may have decided to add a conventional 3-way or 2-way bypass valve setup, just in case the unit was ever replaced with something else. If that’s the case, don’t worry; just leave the valves in their normal “hot water” configuration. 

>>> READ MORE: Winterizing Your RV: Is Antifreeze or Compressed Air Better?

Furrion 2.4GPM Tankless RV Water Heater

This is one of the OEM’s favorite tankless water heaters. Furrion is owned by Lippert (LCI), who’s one of the largest OEM suppliers in the RV industry. Their on-demand water heater has been around for a while, and it works well. It supplies up to 2.4 gallons of hot water per minute, and works at a flow rate as low as 0.32 GPM. That’s quite good – cheaper water heaters may require 0.6-1.0 GPM or more to turn on.

Like most modern RV on-demand water heaters, the Furrion has an adjustable temperature set point. In its case, the range is 95 to 124 degrees Fahrenheit (factory default is 115 degrees). That’s a typical range. Temperatures above 125 degrees will very, very quickly scald your skin. Here’s a table below for reference:

[scalding temperature chart]

How to Winterize the Furrion Tankless RV Water Heater

Operation Manual

Winterizing the Furrion RV water heater does not require a conventional bypass valve system. Instead, Furrion allows you to winterize using compressed air up to 30 psi or liquid antifreeze.

30 psi is … not much. You may find that it’s insufficient to purge the rest of your plumbing system of fresh water. 

If you use the pink stuff, then “antifreeze can be used directly in the water heater,” says Furrion. “Plan for an additional 1 liter to fill the system.” In this case, you would simply pump antifreeze directly through the water heater using whatever pumping method you normally use.

Note that if you do have a bypass valve installed, and if you do choose to simply drain and bypass the water heater, Furrion insists you evacuate the water heater with compressed air first! In other words, you can’t rely on gravity alone to drain the water heater. You have to winterize with either compressed air or antifreeze. 

Precision Temp 550-EC Propane Tankless Water Heater

Although I haven’t worked on or used a Precision Temp water heater myself, I’ve heard good things. The water heater is smart enough to vary the burner output with the flow rate, so it can output anywhere from 16,000 to 55,000 BTUs, which is one of the highest outputs in the industry. It can raise the temperature of the incoming water by up to 88 degrees per gallon per minute, and again, that beats most of the competition.

I do have a slight complaint, but only if you’re retrofitting an existing water heater. The Precision Temp requires a 14.5″ high x 13.5″ wide opening, and the industry standard is 14×14. You may find that some factory openings are a little too short and will need to be enlarged.

Like other advanced water heaters, the Precision Temp “has a built-in thermostat that turns the burner on in low burn when the heat exchanger temperature is about 38° F.” It has a couple of 12-volt heating element that protect the internal plumbing and control valve, but again, the rest of your plumbing system is undefended. 

How to Winterize the Precision Temp Tankless Water Heater

Operation Manual

The Precision Temp manual recommends a 3-step winterization process:

  • Purge the system of water by using compressed air and opening one tap at a time.
  • Fill the system with non-toxic RV antifreeze.
  • When you see the pink stuff coming out of all the hot water taps, you know the system (and water heater) is protected.

If you need to drain the water heater without fully winterizing your RV, Precision Temp says you can just open up the P&T valve. That’s quite convenient. Unlike some other water heaters, here, the P&T valve is located at the bottom of the assembly. I’ve used this trick myself, but!!! –

– turn the unit off first! Make sure you’re disconnected from city water and the pump is off. Open a hot water tap and run the water until it’s cold. Only once your hot water is cold and depressurized should you open the P&T valve. Unless, you’ll scald your skin. 

Precision Temp tankless water heater P&T relief valve location

Fogatti InstaShower RV Tankless Water Heater

My first experience with the Fogatti water heater wasn’t so great, I’m sad to say. One of my customers was in the middle of installing one, and I accepted his offer to take over (bad idea!). I could barely read the manual, which seemed to have been translated by Google Translate after a few too many beers.

I’m pleased to report that Fogatti’s documentation is much improved! (Although the manual still has several syntax errors). Like most of these imported products, the upfront price is great, but good luck getting your hands on replacement parts quickly.

The water heater is sold in two sizes: 42,000 BTU and 55,000 BTU. They produce up to 2.9 gallons of hot water per minute, and the burner should should keep the water temperature within 3 degrees plus/minus of the set point. Like most other tankless water heater, the burner has a built-in thermostat for freeze protection. 

How to Winterize the Fogatti RV Instant Water Heater

Operation Manual

The Fogatti water heater has a drain screw that can be removed to drain the water from the heat exchanger. Here’s the location of that drain screw (see below). The water heater will drain better and faster if you open a hot water tap to eliminate the vacuum. +

Fogatti allows you to winterize the tankless water heater with conventional antifreeze; no bypass is needed. There’s nothing in the manual about compressed air, though. 

Suburban Advantage Tankless Water Heater

Suburban is one the biggest manufacturers of conventional 6-gallon and 10-gallon RV water heaters. In recent years, they’ve also introduced tankless water heaters, both their Advantage (formerly Nautilus) and ST Series. They haven’t released much documentation besides a brochure about their ST Series, but they’re pushing the Advantage Series on OEMs. From what I’ve seen, the Suburban instant water heaters are definitely some of the least expensive (that’s common for Suburban), but that could be a reflection of their mechanical quality. 

Unlike most other tankless water heater, the Advantage model only has a single circular intake/exhaust vent on the exterior wall. This is great … until you need to service the water heater, and you’re paying $100/hr just so someone can crawl inside your cabinet. You’ve been warned.

In most respects, the specifications are rather typical: 0.5 GPM minimum flow rate, up to 42,000/60,000 BTU output, maximum outlet temperature of 113 degrees, heat exchanger protection below 40 degrees … yadda yadda. I haven’t worked on these myself.

How to Winterize the Suburban Tankless Water Heater

Operation Manual

Unlike most of its competitors, the Suburban uses a simple gravity drain. That’s convenient. Here’s what Suburban says: “Remove the service panel to access the drain valve. The drain valve is a red knob located on the rear of the water heater where plumbing enters the water heater.” If you have an -RL model, there are some additional valves and instructions in the manual. 

Once the unit has been drained, you can fill it with non-toxic liquid antifreeze like normal. No bypass is required. 

Camplux RS264/RS264B Tankless Water Heater

The Camplux tankless water heater is a popular aftermarket upgrade for vans and travel trailers. I’ve installed a few myself at customer’s requests.

To be honest, I don’t know if they do their own design or manufacturing. (It did look rather similar to the Fogatti … hmmm.) There must be some factory in China that is making a killing on these tankless water heaters, because I see all kinds of rebranded, private-label water heaters online. But even if Camplux is a private label, they have strong customer service, good online presence, and a decent Owner’s Manual – and that says a lot!

Regardless, it seems like an nice water heater: 2.64 GPM, automatic temperature set point, digital wall control pad or remote control, 0.4 minimum GPM, freeze protection below 43 degrees, and up to 65,000 BTU heat ouput. Those are all respectable numbers! 

How to Winterize the Camplux Tankless RV Water Heater

Operation Manual

Camplux makes winterization easy. You can drain, fill with antifreeze, blow out with compressed air, or use a combination thereof. A bypass valve system is not required, although I would recommend one for versatility.

Here are the instructions from the manual on how to drain the water heater:

“Once the water has been drained,” says Camplu, “the appliance is protected against freezing conditions.” Truth be told, I’m a little skeptical of that claim, because just a few sentences later the manual reads “the water heater must be evacuated with compressed air (see steps above) before bypassing.” That mirrors what Fogatti says, too. 

If you prefer the belt-and-suspenders approach, you can further winterize the unit with either compressed air (up to 30 psi) or liquid antifreeze. Again, plan on one extra liter to fill up the heat exchanger. 

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