Aquahot 400D Issue

[JeromeS13]

Motorhome: 2019 Fleetwood Discovery 38K
System: Aquahot 400D
House batteries: 2 x SOK 206AH (parallel)

I'm having an odd Aquahot issue... We're currently dry camping and using the Aquahot on diesel. Annual maintenance performed in November and have tested the system on diesel several times since. For the most part, everything works as advertised. However, last night (temps in the low 40's), the Aquahot was not igniting. Auxiliary batteries were at about 70% charged (LiFePo4). Tried cycling Aquahot on/off several times. I could hear it trying to start, but it never fully ignites. We're not really close to anyone else, so I fired up the generator at about 0630 this morning (since the wife needs something that resembles hot water for a shower), and bam! The diesel burner ignites and starts working. I verified that in the drawings that the Aquahot uses the auxiliary batteries for power, but no idea why it wouldn't fire last night/this morning... Any suggestions? Thanks!

[bentjm]

What does 70% charged mean when expressed as voltage?

[JeromeS13]

Originally Posted by bentjm

What does 70% charged mean when expressed as voltage?

IIRC, it was around 13.1 volts at the time. However, that's not a good indicator as that will fluctuate with varying loads.

[hilgert]

We have the same Aqua-Hot 400D in our 2019 Discovery, but have not had those issues when on battery (but we are mostly on shore power, less often on battery).

Following to see where this ends up.

[shootist]

Check the voltage entering the aqua hot control board while on batteries/ with the inverter on if it normally is. Then check it when on shore power. If it’s low on batteries you’ll have to find the voltage drop. Fuse is the best place to start. I get low voltage to the fridge once a year or so, cleaning the fuse contacts in the rear run box always fixes it.

[JeromeS13]

Originally Posted by shootist

Check the voltage entering the aqua hot control board while on batteries/ with the inverter on if it normally is. Then check it when on shore power. If it’s low on batteries you’ll have to find the voltage drop. Fuse is the best place to start. I get low voltage to the fridge once a year or so, cleaning the fuse contacts in the rear run box always fixes it.

Thank you for the suggestion. I'm getting House battery +/- .05 volts on the primary + input. However, I also have (apparently) a + input from my chassis batteries as the "optional" input +. This was reading +/- .05 volts compared to the chassis battery voltage... I reviewed the readings from my SmartShunt last night and indeed, the chassis batteries dropped to about 12.23 volts (while the house batteries dropped to 13.15). I'm assuming it opted for the "optional" input voltage instead of the primary input voltage, which also doesn't make sense to me. I'm working on resolving the chassis battery SOC issue... I was using a Precision Circuits Li BIM-225, but I'm having issues with it staying latched 100% of the time. So I've disconnected that and I'm waiting for a Victron 12/12-18 to come in as my charging solution for my chassis batteries while on shore power. If I need to charge my house batteries while off-grid, I'll just use the generator.

[96 Wideglide]

AH 'should' run with as little as 11v.

[JeromeS13]

I did some further troubleshooting... For troubleshooting the diesel burner, the service manual states:

NOTE: Before troubleshooting the Diesel Burner Control-ler, verify that the Aqua-Hot’s Electronic Controller has voltage at both the C1(orange) & C7(white) wires on the JP4 Plug. Both the C1 & C7 wires will only have power when both the Diesel Burner Status Light and the Heating Status Light are illuminated.

Here's the issue: Initially, I do get 12+ volts at C1 and C7. The circulation pumps engage for about 18 seconds, then I can hear the diesel burner ignite for another 18 seconds. However, at that point, the voltage on C1 and C7 drop to around 7.9-8.4 vdc.

Further in the manual, it states:

If the C7 (White - #23) Wire does not have 12VDC, and both the Diesel Burner Status Light and the Heating Sta-tus lights are illuminated, the electronic controller will need to be replaced.

If the C1 (Orange - #22) wire does not have 12VDC Re-fer to the Webasto Diesel Burner Controller Trouble-shooting, in section 10.

It sounds like either 1) this is normal operation and something is telling the electronic controller to reduce the voltage to the diesel burner, or 2) the electronic controller is bad.

I did apply 12+ vdc directly to those pins and everything stays running as normal.

I'm awaiting a call back from Airxcel/Aqua Hot to get their opinion before I spend $561 on a part that may not resolve the issues... Wish me luck!

[shootist]

So the voltage drop happens when the circulation pumps are on? That is still sounding like a power supply problem.

[JeromeS13]

Originally Posted by shootist

So the voltage drop happens when the circulation pumps are on? That is still sounding like a power supply problem.

After talking with Aquahot support, the controller was just doing its job, as something else was telling it to cut the voltage to the burner. He recommended that I take a look at the high limit thermostats. I found that when I wiggled any of the four terminals (two on each of the two thermostats), the resistance across the four would jump around. After connecting/disconnecting all four terminals several times, I ended up with stable continuity across both thermostats. Fired everything up, works like a charm. HOWEVER, after it cycled, it failed to turn on the next time. So, I'm having a second issue and that was with low voltage on the chassis batteries (again). I've since moved a couple of accessories that I had mistakenly installed on the chassis battery side over to the house battery side and my chassis batteries are staying rock solid 100% charged.

I'm still curious as to where the Firefly reads its voltage readings? I would assume from the inputs at the G6A panel, but I've verified the voltage on the backside of my G6A panel and I'm getting within 0.1 vdc of what my smart shunt is reading for chassis and house batteries (at the actual batteries). However, the Firefly sometimes reports as much as 0.4-0.5 volts LOWER than what my shunt is reading.

[shootist]

Originally Posted by JeromeS13

After talking with Aquahot support, the controller was just doing its job, as something else was telling it to cut the voltage to the burner. He recommended that I take a look at the high limit thermostats. I found that when I wiggled any of the four terminals (two on each of the two thermostats), the resistance across the four would jump around. After connecting/disconnecting all four terminals several times, I ended up with stable continuity across both thermostats. Fired everything up, works like a charm. HOWEVER, after it cycled, it failed to turn on the next time. So, I'm having a second issue and that was with low voltage on the chassis batteries (again). I've since moved a couple of accessories that I had mistakenly installed on the chassis battery side over to the house battery side and my chassis batteries are staying rock solid 100% charged.

I'm still curious as to where the Firefly reads its voltage readings? I would assume from the inputs at the G6A panel, but I've verified the voltage on the backside of my G6A panel and I'm getting within 0.1 vdc of what my smart shunt is reading for chassis and house batteries (at the actual batteries). However, the Firefly sometimes reports as much as 0.4-0.5 volts LOWER than what my shunt is reading.

If your firefly is reading voltage from an area further from the batteries it will show lower voltage when a load is present. My water pump will draw my voltage down to 12.6 or 12.7 as shown on the garnet see level as the two are in close proximity and probably the see level was wired in on the same circuit. As soon as the pump shuts off I see whatever my charging voltage is again.

[2cyber71]

I know that my Aquahot 450 sucks the juice. When it’s on it’s drawing heavy juice.
I don’t think my 6 AGMs can handle a period of time by them self, I have AutoGen and my generator kicks in when the Aquahot is going full with all three zones running. I think when it kicks it there is a big amp draw. My AutoGen is set at 12.1 volts.

[96 Wideglide]

Highest draw I've seen on my Magnum remote panel with burner and all heat exchangers / pumps running (other than engine pre-heat), is 17A-DC.