This is more of an informational post in case it could help someone else who experiences this issue.

Back in August, we had a failure of the fan drive gear box in our 2016 Tiffin Allegro Bus, which unsurprisingly, caused the engine to overheat ( post 1, post 2, post 3 ). After this occurred, we noticed that our AquaHot would no longer ignite the diesel burner. The blower would kick on, but there would never be the typical clicks and flame ignition that you’d expect to hear, then the blower would turn off.

It may be confusing on how an engine overheat could impact the AquaHot. It turns out, there is a loop through the AquaHot for the engine coolant to flow through. This serves two purposes:

  • The AquaHot system can be used to pre-warm the engine before starting up on a cold morning.
  • The heat from the engine will keep the AquaHot system hot while the engine is running, preventing the need for electricity or diesel burner use, but still maintaining AquaHot loads ( coach heat, hot water ).

In the AquaHot, there are protections to limit how hot the system can get. This is in effort to minimize the risk of damage to the system and/or personal injury from having the system fluid being way above normal temperature ranges.

From an assumption that the heat is being generated by the electric heating element or the diesel burner, there are two primary protections present:

  • DC High-Limit Thermostats
  • AC High-Limit Thermostat

In my case, one (or both? tough to recall ) of the DC High-Limit Thermostats was tripped, but not the AC High-Limit Thermostat. This meant that the electric heating element would work, but the Diesel Burner would not ignite since it’s blocked by the DC High-Limit Thermostats.

Details on both of these, where to find them, and how to reset them can be found in the AquaHot service manual (found here), on pages 23 and 24.

Once the DC High-Limit Thermostats were reset, my Diesel Burner would ignite and operate perfectly.

NOTE: If an overheat event has occurred, it is extremely likely that the boiler fluid will have overflowed and your boiler fluid level is probably too low. You should confirm this and refill to the proper level before returning the burner / electric element to service.


Michael

Resident Tesla nut and polymath. Raised in eastern Kentucky, joined the US Navy at 19 to operate a Nuclear Reactor on a Fast-Attack submarine. After finishing his enlistment, Michael has continued to follow his passions in technology, astronomy, and of course, traveling the country.

Yes, we’re still alive! – TurtleHerding · 2022-01-27 at 21:30

[…] More details in another post… but the short answer is I had to reset the ‘DC High Limit Thermostat’ […]

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