Annual Maintenance

(400D, 450D, 600D, and 675D)

It is essential to adhere to the manufacturer's recommendations for maintaining your heater to maximize its lifespan. Regular maintenance ensures you receive hot water and heat when you need it most.

FAQs (Aqua-Hot)

What is the difference between Antifreeze and Boiler Antifreeze?

These two are very different. Boiler anti-freeze is intended for use in boiler systems and has a different chemical composition than antifreeze intended for RVs, automobiles and trucks.

Aqua-Hot offers Century Boiler Antifreeze in both green and pink, in 1 gallon and 32 oz options.

If purchasing elsewhere, Camco has pink RV Plumbing and RV Freeze Ban antifreeze in addition to their pink boiler antifreeze; be sure to use the boiler antifreeze in your Aqua-Hot system

Where can I buy boiler antifreeze for my Aqua-Hot system?

Camco pink boiler antifreeze is no longer available directly from Aqua-Hot as well as most RV dealers. Century green and red come in both quart and gallon and is available directly from Aqua-Hot as well as most RV dealers.

*except for Aqua Hot 125D and 125G systems. *125D and 125G systems use a mixture of 50/50 Ethylene Glycol antifreeze and distilled water. Which is available at most big box or automotive retailers.

My propylene glycol antifreeze is discolored. Is this a problem?

Discoloration of propylene glycol antifreeze solution may occur during normal operation of the Aqua-Hot system.  This discoloration does not indicate a malfunction of the Aqua-Hot system or the antifreeze solution.

The following conditions may cause the antifreeze solution in your aqua-hot to change color:


Exposure of the antifreeze solution in the Aqua-Hot boiler tank to air
It is important to keep the overflow bottle filled to the proper level*.  If the Overflow bottle is empty, it must be refilled, and the tank must be bled of air*.  Air in the Aqua-hot boiler tank may cause the antifreeze solution to discolor.


Low Levels of propylene glycol in the antifreeze and water solution
The Aqua-Hot’s antifreeze solution should contain between 35% and 50% propylene glycol.  Operating the Aqua-Hot with less than 35% propylene glycol may cause the antifreeze solution to discolor.  Please see the Aqua-Hot’s Owner’s manual for instructions on testing the level propylene glycol in the Aqua-Hot’s antifreeze solution*.


Adding Tap or Well Water to the Aqua-Hot system
Adding tap or well water to your Aqua-Hot system may cause the antifreeze solution to discolor.  Aqua-Hot recommends using only deionized or distilled water.  Using tap or well water may cause corrosion of the Aqua-Hot system.


Mixing Century Brand (Green) and Camco Brand (Pink) Boiler Antifreeze
Motorhome manufacturers generally fill the Aqua-Hot with Century brand (green in color) or Camco brand (pink in color) boiler antifreeze.  Mixing these two colors together may cause discoloration of the antifreeze solution in your Aqua-Hot.

Discoloration of the Aqua-Hot’s antifreeze Solution does not indicate a malfunction of the Aqua-Hot system or the antifreeze solution.

Which Fuel Filter do I need for my Aqua-Hot hydronic heating system?

Aqua-Hot carries a few different types of fuel filters. Please compare these images with the fuel filter in your coach bay to determine which style you need.

Fuel Filter Brands Information:

Garber R Fuel FilterAqua-Hot Part Number: FLE-120-100

Racor Fuel Filter, R12T Spin-On, 10 MicronAqua-Hot Part Number: FLX-R12-TRA

Inline Fuel Filter, Webasto DBW-2010Aqua-Hot Part Number: WPX-603-359

What does the Low Temperature Cut-Off Thermostat light indicate?

200/250 Models: When the D4 (LTCO) light is off, the unit is up to temperature and ready to make interior heat. When the D4 (LTCO) light is on, either domestic water is being used, or the system is not yet fully up to temperature.

400/450 Models: A green LTCO light means that the heater is up to temperature and ready to make heat. When the LTCO light is not illuminated, either domestic water is being used, or the system is not yet fully up to temperature.

600/675 Models: The LTCO light will always be illuminated and does not impact hot water or heat functions.

How do I winterize the Aqua-Hot Hydronic Heating system?

Please follow these instructions when winterizing the Aqua-Hot’s Domestic Water Heating System:

  1. Completely drain the fresh water storage tank.

  2. Disconnect the domestic water demand pump’s suction line from the fresh water storage tank.

  3. Attach an adequate piece of hose onto the suction side of the domestic water demand pump.

  4. Place the opposite end of the hose into an adequate supply of FDA-approved “GRAS” RV Antifreeze and turn on the demand water pump.

  5. Open and close all interior and exterior water faucets, one at a time, until only pure RV Antifreeze is present. Perform this procedure for both the hot and cold faucets.

  6. Turn off Demand Water pump and remove the hose and reconnect the domestic water demand pump’s suction line to the fresh water storage tank.

An FDA approved “GRAS” rated winterization antifreeze must be used. YOU CANNOT BLOW DOMESTIC WATER COIL OUT WITH AIR TO WINTERIZE AQUA-HOT.

FAQs (Oasis)

What are the advantages of Hydronic heating versus hot air?

Hydronic heating has three advantages over other types of heating systems. These advantages are comfort, efficiency, and versatile installation. Hydronic heating will heat the space more evenly, there is less heat loss as the heat is transferred with a fluid and the heated fluid is easier to move around.

How does the Oasis Hydronic heating system work?

Oasis is similar to a home boiler type of heating system. Our diesel burner however uses the on board fuel supply and operates on a 12 Volt-DC battery power supply. The boiler system then pumps the hot fluid throughout the interior of the motorhome. The domestic hot water is heated “On-Demand” as it is being used. No separate storage of hot water is needed. The main heat source is the diesel-burner. However the Oasis is equipped with one or two 120/240 VAC 1500 watt electric heating element(s) that can provide up to an additional 10000 BTU as well as recover waste engine heat to use in the system. These three sources of heat can all be used at the same time as well.

What is the fuel consumption of the Oasis?

Our Oasis CH50 consumes .44 gal/hr or 1.68 ltr/hr while running and the Combi .33 gal/hr or 1.26 ltr/hr. The heater should however very rarely operate continuously. Typically 1 – 3 gallons of diesel fuel per day will be used for most heating requirements. The use of the electric immersion element(s) also affects this fuel consumption.

What if the heater produces smoke or a smelly exhaust?

Our patented diesel burner should not produce any visible smoke or diesel smell whenever the diesel-burner comes on. If there is smoke present then that is a sign that the heater requires some service or a low DC voltage situation. Please refer to the manual’s troubleshooting section or call our service numbers above.

How often should I service my heater?

The most important thing you can do to prevent some of the common problems is to run your heater periodically like you would do with an engine or generator. A good practice is to operate the heater every 4 to 6 weeks let it cycle off and then switch it off. You should also perform an annual or 750 hour maintenance. This service would consist of a new nozzle filter and O’ring, igniter, air and fuel filter replacement, as well as a thorough cleaning of the combustion chamber, if necessary. In addition to this annual service, be sure to check the level of water and antifreeze solution every couple of months and top off, if necessary.

How do I winterize my Oasis system?

The heating system must be completely drained of domestic water whenever the coach is stored in freezing temperatures and the heating system is not in use. Even if plugged on shore power the BTU output of the element(s) may not be enough. Be sure to follow the step-by-step instructions in your heater’s Owner’s Manual. Either drain the domestic water lines or fill them with an antifreeze mixture.

Can I flush and disinfect my domestic water plumbing system with the Oasis?

Yes, flushing the domestic water plumbing system with pure water is no problem. However, if you are disinfecting the domestic water plumbing system, just be sure to follow proper instructions as this will protect the entire domestic water heating system from serious damage.

How do you use the engine waste heat and preheat function in the heating system?

The natural internal pressure of the vehicle’s engine while in use will force its hot coolant through the engine preheat loop inside your Distribution module or external heat exchanger. If you have an engine preheat switch this does not need to be turned on. However, you should leave the diesel-burner switch on while traveling as this will allow the pump(s) in the heating loop(s) to circulate and disperse the heat from the engine. For preheating the engine an external pump in the engine loop and power switch is needed so the coolant in the engine block circulates through the heat exchanger heated by the Oasis.