Friday, February 3, 2023


Ask Dave: What maintenance does an Aqua-Hot system require?

Dear Dave,
What’s the best maintenance for our Aqua-Hot heating system? It’s not working at the moment, but I’m chasing down a repair tech. —Mike, 2013 Thor Tuscany 45XT

Dear Mike,
Aqua-Hot recommends a monthly visual inspection of the antifreeze/water mixture in the expansion bottle. They also recommend an annual tuneup, for which there is a kit available. Included in the kit are:

  • Fuel filter
  • Diesel nozzle
  • Electrode adjustment tool
  • Burner gasket
  • Portable refractometer
  • 1 quart of concentrated boiler antifreeze

The fuel filter and nozzle should be changed each year. Also the burner chamber should be thoroughly cleaned and inspected.


You will also need a variety of tools such as wrenches and sockets, depending on your model. Most common are:

  • 1/4-in. ratchet
  • 5/8-in. box end wrench
  • 3/4-in. box end wrench
  • 11-mm wrench
  • 9/16-in. wrench
  • 10-in. extension
  • 7/16-in. socket
  • 10-mm socket
  • Phillips head screwdriver
  • Wire brush
  • Pinch-off pliers or clamps
  • Rags and gloves

First step is to turn the unit on and run the heater. Inspect the exhaust to ensure the unit is running properly and let it run for 2 minutes. Verify all functions are operating properly and then turn off the burner. Wait for the unit to cool down properly before going any further and verify the power is off to the unit.

Replace the fuel filter

Use the pinch-off pliers or clamps to pinch the fuel lines at the fuel filter. Remove and replace the filter. Note, it is a good idea to fill the new filter with fuel as it will take several cycles to get a dry filter started.

Remove the pinch-off pliers or clamps after installing the fuel lines. If you do not remove these items, it will blow out the fuel pump gasket.

Restart the burner to purge the fuel in the nozzle area and fuel system. Let it run for 3 minutes, then shut it down and let it cool off.

Clean and inspect burner chamber

Remove the cover by taking off the two top bolts and front bolt. Next, remove the control module, which will just slide off, and disconnect the two wiring plugs.

Pinch off the fuel lines outside the cabinet and remove the metal fuel lines. This will allow you to remove the burner by removing the two I bolts at the 1 o’clock and 7 o’clock position. Slowly remove the burner and rotate it so the nozzle is facing up.

Remove the swirler by pulling straight out. If you have not done an annual tuneup, this might be hard to remove. Use an auto body dent hammer or hook slide hammer. Do not use pliers as this will cause damage to the area where the photo disks sit and cause black smoke during operation.


Clean and inspect the swirler for damage or warping. If there is damage, you will need to contact Aqua-Hot to obtain a new swirler. If the swirler looks good, loosen the 4 swing bolts to remove the combustion chamber. Inspect and clean the combustion chamber with a rag. If it has carbon buildup, you might need a wire brush. An annual tune up will reduce this.

The heat transfer tabs cannot be cleaned with a wire brush. Remove any debris with a wet/dry vac. Do not blow soot or debris out the tailpipe as it could result in blockage.

Reinstall the combustion chamber, new gasket, and swirler.

Inspecting burner and components

Look for any damage to components or excess fuel pooling, which would indicate a leaky fuel pump. Inspect the electrodes for cracks and excess carbon, which can be cleaned with a scrubbing pad.

Inspect the flame sensor or photo eye to make sure it is not cracked, damaged or overheated. Make sure the wires are not damaged and clean with brake cleaner.

Visually inspect the rubber grommets and cutouts to ensure they are not brittle or allow too much air in the cutouts. Check the wiring for solid connections and no bare wiring. Inspect the ears and housing for any cracks or damage.

Replace fuel nozzle

It is recommended you replace the fuel nozzle as the last step. Remove the old nozzle with the two wrenches. Install the new nozzle and seat it properly by tightening with the two wrenches, loosen it, then retighten it. Failure to properly seat the nozzle will cause fuel to leak.

Check and adjust electrodes

There may be a gauge on the side of your burner, or you can use one that is provided in the tuneup kit. Place the gauge on the top of the nozzle so the nozzle touches the plate of the gauge. The electrode probes should sit in the “V” grooves and be flush. An electrode protruding above gauge will cause blue or white smoking. Too low and they will cause intermittent lighting. If the electrodes need to be adjusted, loosen the 10 mm bolt on the side harness, adjust up or down, and retighten the harness.

Reinstall burner

Place the burner back in the combustion chamber carefully without bumping or damaging the electrodes. Swing the bolts back in place and tighten them with the 1/4” wrench so they are not over-tightened. They should not be over 10 inch pounds.

Reconnect the fuel lines, plug in the controller and slide it back against the burner, and replace the cover.

Now run the system. It may take a few cycles to get any air out of the system. Let it run until it reaches temperature and shuts down.

Check antifreeze solution

Unscrew the top of the expansion bottle and use the eyedropper that comes with the refractometer to draw a sample of antifreeze and place it on the meter. It should read between 35% and 50%.

Aqua-Hot has a great tutorial video here.

 You might also enjoy this from Dave 

How do I winterize my Aqua-Hot heating system?

Dear Dave,
How do I winterize our RV? It has an Aqua-Hot heating system and heated floors. —Susan, 2022 Tiffin Allegro Bus 40 IP

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here


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1 month ago

My point of view….crazy amount of things to do. My furnace and water heater do a great job.

1 month ago

I am seeing lots of folks critical of AquaHot. AquaHot is much like your Generator. The more you use, the more reliable it is. I have a 2008 Tiffin Allegro Bus. The AH system is one of the features that I actively searched out and have been very happy with after 5 years of use. The yearly maintenance runs about $250 if you find the right tech and they do it properly.

1 month ago

I have the Oasis brand boiler. After looking through the above Aqua Hot procedures, it made me glad I have an Oasis brand. Much simpler maintenance.

I have found that my system heats as quickly as my propane systems did with the benefit of not having to have a separate fuel source onboard. I have camped in very cold weather and on travel trailers have had to make daily runs to refill propane tanks. Nice to have a system running off my large fuel tank instead.

Neal Davis
1 month ago

Lloyd DeGerald and his son are based out of Arkansas (near Little Rock) but travel to the bigger rallies and do service and repairs to Aqua Hot and Oasis systems. He’s good enough to warrant us going 4 hours out of our way, or more, when traveling so he can fix or service our system (2016-7/2022, Aqua Hot; Oasis, 7/2022-present).

1 month ago

I would avoid these system if I was looking for a new RV. The maintenance plus the real killer is the lag period of a couple of hours to heat your unit to temperature doesn’t make sense. If you stop for the night and it’s 20 degrees out that’s going to be a long time to wait for a comfortable temp in your RV.

1 month ago
Reply to  Crowman

Not sure why you would say that, my AquaHot does an excellent job of quickly heating up the coach. There is no time lag (especially when using diesel as the fuel source). Much more efficient than Propane.

1 month ago

Convinced me that it is one more appliance to avoid if I was shopping for a newer RV.

Bob p
1 month ago

Is all that located in a place where you can comfortably stand or sit with plenty of room for both arms and hands to work on it? Or is it hidden in side a compartment with no room for a large hand to get to it? Lol

Bob M
1 month ago

Seems like oil heat requires to much maintenance and can stop working anytime. I prefer gas heat, very little maintenance and very reliable.

1 month ago
Reply to  Bob M

Have you ever had an older diesel rig park next to you so that you experience the exhaust and jet engine-like sound all night?

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