Aqua Hot suddenly not heating?

[Roger Milne]

So the Aqua Hot suddenly quit running on the Diesel Burner side a couple days ago and I found the return hose from the expansion tank to the pressure cap had split and drained the expansion tank. So repaired that and topped up the tank with about 1/2 gal of Propylene Glycol.

All indicators on the control module are showing green, but when I flip the kitchen panel diesel switch to "on", the indicator comes and the burner lights off, but then turns off and goes through its purge / cool down cycle and after that the indicator light in the kitchen panel goes out. The switch is still in the "on" position and the #3 Stir pump still runs as indicated on the control panel, until I switch the off in the kitchen.

I have checked the expansion tank since running it and it seems to have drawn in about 1/4 of a gal based on the fact I filled it to the "hot" line and it now shows half way full between the Cold and Hot marks.

There's no Red indications on any of the system monitor lights, so I don't know if I have air in the system or if something else is going on. I'm currently away from the RV for the next 14 days and my wife can use the electric element for hot water, but I wanted to see if I maybe missed something or what direction of troubleshooting I need to take when I get home.

[Fred Brooks]

    Roger,
  One of the possibilities could be the "float switch" inside the coolant reservoir. If it has detected low coolant, it will give you the symptoms you are experiencing. Turn off the electric and let the coolant cool off and remove the radiator cap. If the coolant is not right there in the neck, add coolant. Hope this helps, Fred

[Roger Milne]

Thanks for info. I’ll look into it and see if that helps.

[Joel Ashley]

To Fred's comments:
The float switch in my HydroHot wore/broke a few years ago.  It wasn't something I could dig out of the top of the tank, but if you lower the coolant level to below the switch port, you can remove the switch (the float may not be with it if it broke off).  Replacement switch/float assemblies, as I recall, are "rare" but available from certain vendors.  My replacement was an improved version as I recall, and less likely to "disintegrate" and or the float leak.

The job was messy, but I finagled a drain line from the drain port down and out an existing nearby hole in the bay floor.  Sans that it could've been worse.  I probably followed instructions proffered on a YouTube video, but recall my configuration was slightly different, requiring some common sense thinking.  I know I was concerned about the missing float part sashaying around inside the tank, but ultimately decided, after failed fishing attempts through the top, that it wouldn't interfere with operations.  It's imperative that everything be kept clean, like around the top cap/port and the switch port.  You don't want dirt or debris getting in the tank.  Properly done, you can reuse the fluid you have to drain to get below the switch port. 

It was a matter of getting just the right deep socket as I remember (finally found at Autozone) - and I had to modify it to accommodate the new switch's wires, carefully balled up and stuffed inside undamaged while turning the wrench.  Then it was just a matter of hooking up a couple of wires.

I think a person can jumper a couple points on the board and bypass the float switch until you have time to do the repair or get it to a service facility.  I apologize for my dim and aged memory, but others here may offer further details.   And somewhere I think I have pix of my fix that I'll try to add.

Joel

[Joel Ashley]

Hydronics float switch photo and tank drain location photo.

[Roger Milne]

Hydronics float switch photo and tank drain location photo.

Thank you for that info. I’m away from the RB for the next 10 days but will defintely look into it when I get back. Thanks for the heads up. Hoping that’s the problem.

[Joel Ashley]

“ There's no Red indications on any of the system monitor lights, so I don't know if I have air in the system or if something else is going on.”

If there is no warning red lamp on the low coolant indicator on the black monitor panel in the hydronics bay, then the implication is that what Fred and I proposed may not be the issue.  But if the lamp is red, then you can jumper the top right two terminals on the panel board.  A simple paper clip may do it, but I personally would use a little more sophisticated or electrically aesthetic and secure approach.  Keep in mind that this would be only a temporary “fix”, that left in place could endanger your entire device should coolant actually become very low in the tank.  Permanent repairs should be prioritized.

Here is a link to a more detailed document you should print out and keep with your hydronics manual(s) for future reference, even if it’s not the issue this time.  Keep in mind that the illustrations therein might not exactly match your unit, and there may be other ones and online videos out there that are more specific to yours.

https://wiki.foreforums.com/_media/technical:aquahot:how_to_defeat_float_switch_-_2-2009_.pdf

-Joel

[Eric Maclean Co-Admin]

Roger
You stated that the aqua Hot burner comes on with the switch and that it runs for a little while and then and runs a purge cycle and shuts off followed by the light in the switch going out.
Are you sure that the burner actually ignites or are you just hearing the blower run while it runs through the purge cycle ,tries to ignite and run through another                 purge cycle and shuts down.
The little processor that runs the aqua Hot burner is set up to ignite using a small ignition coil and a pair of electrodes, the burner will run through a per cycle first to make sure there's nothing combustible in the combustion chamber and then it opens the fuel solenoid and runs the igniter ignition coil to ignite the burner.  if the photo cell in the burner arrangement does not see a light ie a burning flame the controller then shuts down the fuel solenoid valve and runs a purge cycle after which it turn off the lamp in the switch notifying you that the burner has failed to ignite.
 it will stay this way until the next time you turn the switch off and then back on.
The alcohol is a wonderful unit when it works but it does require regular maintenance to make sure that it works efficiently and well.
The first thing to do would be to do a full service on the burner this requires removing the burner head to access the combustion chamber and burner tube the burner tube can then be removed and cleaned along with the burner chamber itself it's common for these to get suited up which creates all sorts of problems with the burner. As part of the service it would be a good idea to replace the burner spray nozzle as these are aware item and should be done annually. Of course the new fuel filter should be installed and the ignition electrode alignment and GAP should be checked apart from that there isn't a lot to do on a servicing and like I said it should be an annual event once you become familiar with the system it isn't all that daunting the hardest part is getting the cover off to get to the burner.

There are several faults that can result in a non-ignition event or a flame out.
1) lack of spark or bad ignition coil dirty ignition electrodes or electrodes that are not gapped properly.
2) lack of fuel possibly a plugged fuel filter plugged nozzle or a bad nozzle spray pattern.
3) a photocell that is inoperative or just plain suited up so it can't see that the light of the flame.

You should be able to find the manual for your particular aqua hot model number in the coach assist library that manual will walk you through the complete service and repair of the unit.

Hope this helps
Eric