A couple of weeks ago I noticed a slight smoking of my Aqua-Hot on initial startup after it had been sitting for a while, week plus. It would clear up immediately but it bugged the hell out of me. We were just starting a week long trip and that didn't get it off on the right foot. The next morning when the burner kicked on it was perfectly clean again. I thought that was odd so I figured I would perform a service on it when I returned home. The remainder of the week long trip in Grand Teton NP was perfect.
Upon arriving home I performed the maintenance and when I removed the nozzle from the blower assembly I found it odd that I had fuel that had puddled in the area under the nozzle. I replaced the nozzle, fuel filter and cleaned the combustion chamber which actually was still very clean from the last service, barely discolored actually.
I fired the unit up and it smoked a bit upon startup which I could see due to the puddled fuel under the nozzle. It cleaned up rather quickly, within about a minute or so, and then burned perfectly clean for the remainder of the cycle.
I shut the system down and didn't run it again until our trip to Glacier NP last week. Again, first day out after it had been sitting for several weeks it smoked upon initial startup and cleaned up within a minute or so. I felt like there was an issue with fuel not being shut off completely so I ordered a fuel solenoid rebuild kit. When we arrived home the rebuild kit was awaiting us.
I replaced the components and upon removing the plunger from the solenoid valve I think I discovered the issue. At the very end of the plunger where it contacts the pintle it was indented slightly. There is not a lot of spring pressure holding this valve closed so any slight variation in the seat/pintle could potentially allow fuel to seep past.
Upon completion it fired right up and was clean upon startup. I let is sit for several days and fired it up to find it was perfectly clean upon startup, problem solved.
I should have taken pictures of the process but I am putting together a youtube video of the procedure/process.
Here are the parts in the fuel solenoid rebuild kit.
Indent at the end of the plunger. This was the cause of the leak after many years of use.
All in all a pretty easy and straight forward repair. I will post a link to the video when my son completed the editing of it.