Keeping the Aqua-Hot system in your coach tuned is an uncomplicated annual task. Slow and incomplete fuel burn (displayed by black smoke from the unit’s exhaust) is the “tell-tail” sign of the system’s need for an annual tune up.

We started by downloading the shop manual found on the manufacturer’s web site: www.aqua-hot.com. The manual is complete, giving clear descriptions of the parts, part numbers and procedures for performing the recommended annual maintenance.

Following the recommendation outlined in the manual, we turned off the power to the unit’s head and located the two eyebolts (roughly located in the one o’clock and seven o’clock positions of the unit) securing the diesel burner head to the blower housing. We carefully lifted the unit out and away from the blower housing exposing the ignition electrodes, photo disc and fuel nozzle. We found enough slack in the fuel and electrical connections that we did not need to disconnect them to service the unit. We simply pulled the unit back and carefully rotated it into position to gain access to the parts we wanted to work on.

Connecting jumper wires to the ignition electrodes is the next order of business. This is a necessary safety procedure to prevent accidental shock and/or fire while working on the unit.
The blower housing and combustion chamber are now also exposed. Lift (pull) out the combustion chamber to clean excess carbon and soot. The blower housing can be carefully cleaned using low-pressure compressed air and/or wiped down. Reinsert the combustion chamber when cleaning is completed.

Taking a small piece of Scotchbrite® material, carefully remove any varnish built up on the electrodes (changing the color from dull brown to shiny silver). Be careful to not bend or move the electrodes’ position, if you do you will need to reposition the electrodes using an electrode adjustment gauge.

The fuel nozzle is a precision calibrated part and cannot be cleaned or serviced. We replaced our unit’s fuel nozzle using a standard 3/4-inch box-end wrench to hold the fuel nozzle housing and a 5/8-inch box-end wrench to remove and replace the nozzle. Be sure to use care when handling the new nozzle. Dirt and oils from your hands as well as dirt and dust from cleaning the unit’s burner housing can partially plug the nozzle’s orifice, restricting fuel flow which will have a negative effect on the combustion process. When replacing the fuel nozzle, be sure to tighten the nozzle, back it off one-quarter turn and firmly retighten. Following the procedure will establish a seated fit and avoid leaks according to the manufacturer.

The flame sensor is a photosensitive device, which supplies the diesel burner’s control unit with a DC voltage signal when it detects a flame (light source). Cleaning the flame sensor is recommended. For light dust, dirt and/or carbon deposits, wipe the sensor with a clean soft cloth. For heavier deposits, the manufacturer recommends removing the sensor from the photo disc and cleaning it with brake cleaner.

Once the cleaning was complete and the parts were replaced, we removed the jumper wire from the ignition electrodes and careful lifted the unit back into position. Starting the eyebolts by hand, we tightened them alternately, fully seating the diesel burner head to the blower housing. Do not over tighten the bolts. The manufacturer recommends 20 to 40 inch pounds.

Now that the unit’s components are cleaned or replaced, the only item left is to replace the fuel filter supplying diesel fuel to the Aqua-Hot unit. On our coach the filter is located inside the passenger side fuel fill compartment. Access to the filter is gained by removing the two screws under the coach holding the fuel door side panel in place. Lift the door (side panel) up and secure it, exposing the fuel filter. Our unit uses a Racor.

Start by removing the old filter, spinning the assembly counter clockwise. Be sure to place a small catch basin below the filter to contain any spilled fuel. Once the filter assembly is removed, pour the remaining fuel into the catch basin and remove the Lexan water separator bowl from the upper half of the filter. Make sure to remove and discard all old gaskets and O-rings from the filter base (attached to the coach) and the Lexan bowl. Using a clean cloth, wipe the Lexan bowl clean. Using a small amount of clean diesel fuel, lubricate the new O-ring and place it in the groove on the Lexan bowl. Screw the Lexan bowl and new filter body together. Next lubricate the filter body gasket with a small amount of diesel fuel and place it on top of the new filter body’s groove. Now fill the new filter body with clean diesel fuel. It is highly recommended to always fill diesel fuel filters before installing to “prime and purge” the system. Carefully thread the new filled filter assembly to the filter mount. Before securing the side panel in place, start up the Aqua-Hot unit and inspect for leaks, there being none, secure the side panel with the two screws.

Taking the time once a year to tune up your Aqua-Hot’s system will assure efficient operation and the benefits of all the systems features for the coming season.

Sources:
Vehicle Systems, Inc
15549 East Highway 52
Fort Lupton, CO 80621
800-685-4298
www.aqua-hot.com