Discovery: Aqua-Hot Thermistor

[jbellarmada]

Started getting a fault on my 400D. “Thermistor Reading Invalid”. I can reset and the fault is cleared and doesn’t come back….until some time later. I have been doing the reset using the VegaTouch Mira panel. Unit is in a 2020 Discovery LXE 40G. This is happening when we are filling a bathtub which takes about 30min under Diesel burner mode.

Can’t find any info to help me understand what thermostat to check and/or replace.

Can anyone direct me to further info on this error?

Thanks

[jbellarmada]

Did further review of the situation and the AH panel on the unit did seem to fail, burner stopped at 180 and that status reported fault. The fault screen was blank. After returning to the Home Screen the unit showed status OK and the burner restarted. It then started to reheat the coolant again but not until it fell below 170. This problem repeated, as it started to reach 180 it failed and fell back to 170.

[Topperace]

Well good you found problem, hopefully that’s all that is wrong with it.

[jbellarmada]

Not sure I found the problem. It seems to recover from the fault but that tells me there is a problem and it will likely continue until the unit does not recover from it. I guess I will call Aqua-Hot, figured someone here would have seen this fault before.

[Cincy Steve]

Try replacing your high limit thermostats.

Had a randomly, reoccurring issue where unit would quit but then restart (manually) & run normally for minutes….or weeks before failing again. Lots of reading & several messages from an experienced tech & I had compiled a lengthy list of potential problems & the assurance that diagnosis, sight unseen, would be very difficult.

While ordering parts for annual service, I also ordered high limit thermostats, because they were on sale & appeared on the potential problem list.

It has now been 3 years without a recurrence. Coincidence or wildly lucky guess?

[jbellarmada]

Ordered one and will give that a try. Thanks! They say to service the filter and nozzle annually. I have been doing this but probably wasting money as some years we are only in the Coach 2 weeks! Are you servicing annually or sort of thinking about hours of operation to decide when it is time? Or waiting for failed ignitions to start?

[Cincy Steve]

I service the unit every year. For $50 in parts & a couple hours of time, I consider it cheap insurance. We’re in ours for 10-12 weeks/year & for a significant amount of that time we need the burner for heat.

[JohnKoz]

So jbellarmada, did the new thermistor solve your issue?

-john

[jbellarmada]

No, appears to be a firefly integration problem. The errror has not been found on the aqua-hot diagnostics, only in the firefly panel and mobile app

[sks691]

jbellarmada, was this issue solved? I have a similar issue with my 2025 Renegade and it seems to be the firefly panel and not the actual Aquahot.

[jbellarmada]

Yes and no. Still happening but again no error on the AquaHot panel at all, just the Firefly. Seems to be a false alarm but very annoying