The Heat is ON

Aqua-Hot burner assembly
Photographer: Jenn Gehr
Removing the nozzle from the Aqua-Hot burner assembly requires the use of two wrenches, one on the backing nut and one on the nozzle.

It seems like Murphy’s law applies just when we least expect it. For furnace operation, it’s usually when the temperature plummets and heat is needed to keep warm. Nearly every motorhome is equipped with some type of a forced air unit. Whether the furnace runs on LP-gas or diesel fuel, every model requires an annual visual inspection and a bit of maintenance to keep heat flowing without interruption.
Many safety features are built into today’s modern furnaces, and sometimes they are at fault when normal operation is interrupted. The majority of furnace problems are a result of, or combination of, low gas pressure, low voltage, inadequate ducting, insufficient return air and lack of annual maintenance. Be sure a certified RV technician completes any repair work that is beyond cleaning and inspections; improper repairs or adjustments can lead to a hazardous situation. Before inspecting the furnace and/or making repairs, make sure the LP-gas and the thermostat are turned off.

Visual Inspections

Using a bright flashlight, check for any debris or mud dauber nests residing in the intake or exhaust vents. Remove any obstructions with an appropriate tool. Soot is a product of poor combustion, possibly caused by a spider web, mud dauber nest or rust in the burner. The furnace will need to be repaired by a technician if you are uncomfortable with removing these obstructions. Do not use the furnace until it’s been repaired.

A refractometer is used to test the percentage of propylene glycol in the Aqua-Hot system’s antifreeze.
A refractometer is used to test the percentage of propylene
glycol in the Aqua-Hot system’s antifreeze.

Most furnaces do not come with a lint or dust filter, which is commonly used in residential homes. This lack of filtration leaves furnaces unprotected and is the main reason annual inspections are recommended. On the flip side, never install a filter at the cold air intake, as it will restrict the return air.
For further inspection, remove or open up the access door or panel to allow for a full visual of the front of the furnace. Look for dust and lint buildup and be ready to remove it using moderate air pressure or a vacuum cleaner. Also, check all of the interior components and blower wheels. Heavy lint buildup can cause the blower wheels to rotate out of balance, thus causing premature failure of the blower motor.
Check the circuit board for lint, dust and corrosion. Don’t use high air pressure on a PC board; too much air pressure can damage the components. Canned compressed air or a vacuum cleaner works well for this type of cleaning.
Heat ducting can fill with a large amount of dust and lint. Use a vacuum cleaner or a high volume of air to clean these ducts thoroughly. Inspect the ducting at the furnace, making sure each hose is attached and has not been crushed or damaged. Over a period of time, heat ducts can become brittle and split, routing highly heated air into the wrong area.
Low LP-gas pressure can result in furnace ignition failure and/or poor operation. The LP-gas regulator may need to be adjusted or replaced by an RV service technician who can properly set the gas pressure on the regulator for optimum safety and function.
Low voltage can slow the fan speed below the threshold for furnace ignition. The fan may sound fast enough but will not trip the sail switch, which is a safety device. If you suspect the voltage is too low, start the motorhome engine or AC generator to boost the battery voltage and try the furnace again. If this solves the problem, this could be a sign that the motorhome batteries have seen better days, or there are loose or corroded connections in the wiring. Voltage can be checked at the furnace using a multimeter. The furnace requires a minimum of 10.5 volts DC to allow the fan to run fast enough to trip the sail switch.
Bug screens are a popular aftermarket item designed to cover the intake and exhaust vents. However, manufacturers do not recommend the use of such screens as they can become plugged and restrict the flow of air, which can result in poor combustion. Keep in mind that bug screens will not stop a small spider, but if you need them to prevent those pesky mud daubers from moving in, an alternative is to block the vent with something that can be removed prior to your next outing. It’s critical that any vent blockage be cleared before using the furnace.
Aqua-Hot comfort and water heating systems are found in a number of high-end coaches, most commonly in diesel-powered motorhomes. The Aqua-Hot system has a different service and inspection process than standard RV furnaces. Inspection is limited to checking the antifreeze (propylene glycol) level and the visible fuel and rubber hoses. It’s a good idea to check each of these before every outing; a 10-second visual inspection just might save your weekend.
Annual service consists of replacing the fuel nozzle, a commonly overlooked item, and the inspection of the burner assembly while replacing the nozzle. Replace the fuel filter annually as well. It’s best to carry a spare fuel filter at all times just in case you encounter a bad batch of fuel. Annually check the percentages of propylene glycol in the antifreeze and water solution. If you are unable to test this level, take a small sample to a qualified radiator shop for an accurate reading.
Chances are you’ve traveled in the spring, winter or fall and have needed the furnace to help combat the chill of the morning or for regular temperature control throughout a colder night. Annual inspections and regular furnace maintenance procedures can keep that chilly air outside where it belongs.


Source teamed up with Bilstein engineers to custom tune/build these exclusive Platinum Series high-pressure-gas shocks. REK-206 kit provides a pair of 60mm front shocks and 46mm rear shocks to replace the smaller, 40mm factory Sachs hydraulic shocks.


Source Platinum Series Bilstein shocks (left) utilize a much larger piston inside the shock tube than the factory hydraulic shocks on the Freightliner XC chassis. The Bilsteins also provide far more suspension compression and rebound damping control under all driving conditions.


About the size of a pack of gum, this Ride Control Valve regulates airflow in and out of each air spring to smooth out the chassis rocking and rolling. The proprietary metering design lets air out quickly, but slows it down returning into the air bag.


Removing the OEM Sachs rear shocks on the Discovery only required dexterity and an air impact with a 11⁄8-inch socket.


Master technician Todd Hill showed us how Source’s Platinum Series shock (left) compares to the factory Sachs rear shock. The two look similar in size. But the Sachs shock (right) is a twin-tube, while the Bilstein is a high-pressure-gas single tube, so the piston and valving, which control the suspension, is about 50 percent larger on the Bilstein.


Hill leaves the retaining band on the high-pressure gas-charged Bilsteins during installation. This eases the install. The thin plastic band breaks as soon as the motorhome suspension flexes.


After the new shocks are installed, a Comfort Ride Control Valve is placed on each feed line to the rear air springs. The air lines were cut and the ends then inserted into the valves to lock them in place. Valves are directional, so they must face the proper direction (indicated by the arrows) for correct airflow.


Swapping out the front factory Sachs shocks for the bigger 60mm Source Platinum Series Bilsteins requires using a ¾-inch socket up top and a 11⁄8-incher for the bottom mount. Hill installed the Comfort Ride air spring control valves after the new shocks were mounted on each side.


Installation of Source Engineering’s Freightliner XC rear sway bar only requires removing the four 43mm nuts from the trailing-arm bolts. A special wobbly socket is used to handle this task.


Source Engineering’s REK-206 sway bar assembly is lifted up and over the exposed trailing arm bolts, where it will stay positioned by itself until the bolts are reinstalled. The design is simple, yet efficient in reducing body roll on big motorhomes.


After the sway-bar assembly is in place, the trailing-arm nuts are replaced and torqued to spec. Installing the sway bar takes less time than replacing one of the rear shocks.


Source Engineering’s Freightliner XC rear sway bar contributes a significant amount to the overall ride improvement. The side plates are 5⁄8-inch steel and the torsion tube is a hefty 1¾-inch diameter.


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