Frequently Asked Questions

Antifreeze and boiler antifreeze.

These two 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.

Antifreeze and coolant 

These terms are typically used interchangeably. Aqua-Hot heating systems use boiler-designated antifreeze that is rated GRAS — Generally Regarded As Safe.

GRAS

This is the Federal Drug Administration term for Generally Regarded As Safe. GRAS is the term to look for on antifreeze products. Anything else is likely to be harmful if swallowed.

Freeze Point is the temperature ice crystals will start to form in the antifreeze solution.

Burst Point is the temperature where damage will occur to the coach.

Propylene Glycol Boiler Antifreeze In 2002, Aqua-Hot changed the system design and in 2003 systems started using Propylene Glycol-based boiler antifreeze rated Generally Regarded AS Safe (GRAS). *except for Aqua Hot 125D and 125G systems.

All Aqua-Hot Systems manufactured after 2002 must use Propylene Glycol antifreeze, including Hydro-Hot™, Aqua-Hot 250P™, Aqua-Hot 250D™, Aqua-Hot 375D™, Aqua-Hot 375LP™, Aqua-Hot 400D™, Aqua-Hot 400P™, Aqua-Hot 450D™, Aqua-Hot 525D™, Aqua-Hot 600D™, and Aqua-Hot 675D™. DO NOT use Ethylene Glycol or Propylene Glycol automotive antifreeze in these Aqua-Hot systems.

Ethylene Glycol Antifreeze Ethylene glycol antifreeze is toxic, does not have the GRAS label and is not suitable for an Aqua-Hot system manufactured after 2002. Ethylene glycol was used in pre-2002 Aqua-Hot systems with the exterior domestic hot water loop design. Ethylene glycol can be used in these pre-2002 systems, as well as GRAS-labeled propylene glycol boiler antifreeze.

*125D and 125G systems use a mixture of 50/50 Ethylene Glycol antifreeze and distilled water.

Unlike automotive antifreeze, boiler antifreeze has a higher boiling point and higher viscosity that helps lubricate the system, as well as the rust, scale and corrosion inhibitors. When properly used, it is capable of efficient and high heat transfer.

Aqua-Hot heating systems use either the Century or the Camco brand products. The color your system has depends on the coach manufacturer and the model year of your motorhome.

*except for Aqua Hot 125D and 125G systems. *125D and 125G systems use a mixture of 50/50 Ethylene Glycol antifreeze and distilled water.

Aqua-Hot heating systems typically use either the Century or the Camco brand products. The color your system has depends on the coach manufacturer and the model year of your motorhome. TIP: Don't mix colors in your Aqua-Hot system. Mixing pink and green boiler antifreeze produces a brown color that may be confused with corrosion, creating unnecessary service expense.

*except for Aqua Hot 125D and 125G systems. *125D and 125G systems use a mixture of 50/50 Ethylene Glycol antifreeze and distilled water.

Antifreeze Brands Information

You can check the antifreeze color by looking at the expansion bottle for your Aqua-Hot heating system or draining a little from the drain valve. Aqua-Hot heating systems typically use either the Camco (pink color) boiler antifreeze or the Century (green color) brand products. The color your system has depends on the coach manufacturer and the model year of your motorhome.

Camco pink boiler antifreeze is available directly from Aqua-Hot as well as most RV dealers. Century green is available directly from Aqua-Hot.

*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.

Antifreeze Fill levels are visually checked at the expansion bottle when the Aqua-Hot system is warm and level; the proper fill level is at the HOT line. 

Run your Aqua-Hot system to operating temperature. When it is warm and the coach is level, visually check the Aqua-Hot expansion bottle to see if the antifreeze solution is at the HOT mark. This gives you a true indication of the Aqua-Hot antifreeze solution level.

Check the percentage of propylene glycol antifreeze solution in your Aqua-Hot system with a calibrated coolant/antifreeze refractometer. Water will evaporate from the boiler antifreeze mixture over time, concentrating the antifreeze mixture and changing the ratio in the system.

The Aqua-Hot antifreeze solution should fall between 35% and 50% propylene glycol boiler antifreeze to water. Too much antifreeze lowers the heat transfer capability, causes sticking check valves in the heating zone lines and may coat the system's interior surfaces resulting in lower water and interior cabin temperature levels. DO NOT exceed 50% propylene glycol in an Aqua-Hot system.

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.  

*Please see Aqua-Hot Owner’s and Service Manuals for instructions concerning all of the above items.  These Manuals are available on the library page at www.aquahot.com

Aqua-Hot does not recommend draining and flushing the system unless the wrong type of fluids were added to the boiler fluid.

For example, if your system uses propylene glycol “GRAS” antifreeze, but ethylene glycol was mistakenly added, the system would need to be flushed for safety reasons.

60,000 BTU/h

Use the Propylene Glycol-Based Antifreeze Protection chart to determine the protection you require in your Aqua-Hot system. Freezing Points are temperatures at which ice crystals form. Even below those temperatures, a slushy condition exist which may flow. Burst point is the temperature where damage will occur to the coach; at antifreeze solution percentages above 35%, burst protection is below -50 degrees F.

The propylene glycol antifreeze level of the solution in the Aqua-Hot heating system needs to fall between 35% and 50%. The Freeze Point is the temperature at which ice crystals will start to form in the antifreeze solution. Burst Point is the temperature where damage will occur to the coach.  DO NOT exceed 50% Propylene Glycol in an Aqua-Hot System.

Inspect your Aqua-Hot system monthly. Run your Aqua-Hot system to operating temperature. When it is warm and the coach is level, visually check the Aqua-Hot expansion bottle to see if the antifreeze level is at the HOT mark. This gives you a true indication of the antifreeze solution level.

When you need to add antifreeze, determine the freeze protection you need in the final antifreeze solution and mix your replenishment solution accordingly. This will require a refractometer for accuracy.

After you obtain boiler antifreeze with the same color as your current system, it is critical that you determine the antifreeze mixture of the Propylene Glycol boiler antifreeze in your system. Water will evaporate from the boiler antifreeze mixture over time, concentrating antifreeze mixture and changing the ratio in the system. 

Use a calibrated coolant/antifreeze refractometer and measure the ratio of Propylene Glycol in your antifreeze solution. 

Caution: Automotive “ball type” hydrometers that measure ethylene glycol in the engine’s coolant system will not properly measure propylene glycol.

The correct antifreeze solution mixture for protecting your Aqua-Hot system depends on where you are and how cold it is — or can be. 

Use the Propylene Glycol-Based Antifreeze Protection chart to determine the protection you require in your Aqua-Hot system. Freezing Points are temperatures at which ice crystals form. Even below those temperatures, a slushy condition exist which may flow. Burst point is the temperature where damage will occur to the coach; at antifreeze solution percentages above 35%, burst protection is below -50 degrees F.

Aqua-Hot recommends the antifreeze solution contain between 35% and 50% propylene glycol boiler antifreeze to water mixture. Too much antifreeze lowers the heat transfer capability, causes sticking check valves in the heating zone lines, and may coat the system's interior surfaces resulting in lower water and interior cabin temperature levels. DO NOT exceed 50% propylene glycol in an Aqua-Hot system. 

Your Aqua-Hot Factory Authorized Service Center will assure the proper ratios. If you do it yourself, check the color.

Green Color Ratio? The green color Century brand boiler antifreeze is pre-mixed at approximately 37% propylene glycol and requires NO dilution and it is not necessary to mix Century boiler antifreeze with water before adding it to the Aqua-Hot system’s antifreeze solution.

Pink Color Ratio? The pink color Camco boiler antifreeze comes two ways: There's a pre-mixed gallon and a concentrated quart.

The Camco pre-mixed gallon has approximately 67% propylene glycol. DILUTION IS REQUIRED to achieve the proper antifreeze to water ratio. Add one (1) gallon of Antifreeze to one (1) gallon of deionized or distilled water to reach a 35%-38% Propylene Glycol Level. Check the diluted level of Propylene Glycol with a refractometer before adding the new solution to the Aqua-Hot system antifreeze solution.

The Camco 32oz. concentrate contains approximately 97% propylene glycol. DILUTION IS REQUIRED. Add one (1) quart of Antifreeze to two (2) quarts deionized or distilled water to reach a 35%-38% Propylene Glycol Level. Check the diluted level of Propylene Glycol with a refractometer before adding the new antfreeze solution to the Aqua-Hot system.

TIP: Don’t mix colors in your Aqua-Hot system. Mixing pink and green boiler antifreeze produces a brown color that may be confused with corrosion, creating unnecessary service expense. Camco and Century may not honor the warranty of their product if mixed with another company's product.

Camco and Century may not honor the warranty of their product if mixed with another company’s product. 

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.

When your visual inspection level indicates a need to replenish the antifreeze solution:

1. Use the same color boiler antifreeze that’s in your heating system.

2. Determine the Propylene Glycol antifreeze protection level you want, using the chart below.

3. Make sure you have the antifreeze amount you need to fill your system to the HOT mark on the expansion tank. See back for details on mixture for your color of antifreeze.

4. Bring your heating system to operating temperature. This prevents the overflow that will happen when coolant is added to a cold tank.

5. Remove the expansion tank cap. TIP: Solution in the system is very, very hot.

Wear eye and skin coverings to protect against splashes or spray.

6. When refilling, open the Air Release Valve located on the expansion tank connection on the Aqua-Hot system to release air pockets; close the release valve when antifreeze appears at the Air Release Valve. Fill until you reach the HOT mark on the expansion tank.

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