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Old 11-24-2022, 08:17 AM   #1
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Strange AquaHot Problem...

Thought I would pose the question to the group on the off chance that one of you has seen this issue before...

Our HydroHot HHE-500-09 works just fine on the diesel burner. The electric heating element, however, has failed over time (will explain) and now trips the 120V 20A circuit breaker every time I switch it on.

Initially we noticed that the hot water would last for a shorter time than normal when showering. That lead to no hot water using the electric element only, but the breaker never tripped. Now we have progressed to the point that the breaker will trip as soon as I switch on the electric heater.


The service manual shows only 3 components in the AC heater circuit: the AC relay, the AC high limit switch, and the heating element itself. I've been troubleshooting all 3 components with the following results:
- AC relay: Working as it should. 12VDC on the primary pins, and continuity between the secondary (AC) terminals when I switch on the electric heater.
- AC High Limit: With the AC leads disconnected from the AC relay, I can read continuity from the lead that connects to the relay through the high limit switch to the heating element terminal.
- Heating element: With all leads disconnected I read 9.5 ohms across the terminals. This indicates a GOOD heating element.
I also measured resistance from the AC relay lead (the one that goes through the limit switch to the heating element) with the heating element connections in place. I get 9.5 ohms to the AC input Neutral lead (normal) and about 2K ohms from the AC relay lead to the AC input ground (copper) lead. All of this seems normal and indicates a good AC heating element.


I called AquaHot tech support and they can't think of any other test that I have not done already. Admittedly, this was their level 1 tech support guy who suggested I change the heating element, and if the problem persists, then call back and speak to their 'level 2' guy.


I'm not a big fan of the Air Force troubleshooting method (swap parts until it works ) especially since changing the heating element is such a pain in the wazoo. Wondering if anyone has seen this type of problem on their AquaHot / HydroHot system and was able to resolve it?
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Old 11-24-2022, 08:31 AM   #2
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You can bypass the high limit by installing a fuse in between the connectors. You can turn it on and see if it trips the breaker.. You can disconnect the leads on the relay with the thermostat jumped and then turn on the unit. Make sure you protect the leads you disconnected. If it doesn’t trip the breaker, then you have an issue at the electric element.
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Old 11-24-2022, 08:57 AM   #3
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Quote:
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You can bypass the high limit by installing a fuse in between the connectors. You can turn it on and see if it trips the breaker. But that only controls when the the relay is told to turn on the off the element. You can disconnect the leads on the relay with the thermostat jumped and then turn on the unit. Make sure you protect the leads you disconnected. If it doesnít trip the breaker, then you have an issue at the electric element.
Thanks Bobby. Along this same path but working backwards towards the relay... I think I can just disconnect the neutral lead from the heating element and see if the breaker trips. That would test the path through the high limit and heating element. If that fails, then disconnect the heating element input and see what that gives me. If the breaker stays good then I know for sure it's the heating element. Still weird to me that resistance would measure out good while there is another path to ground that trips the breaker....
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Old 11-24-2022, 09:10 AM   #4
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Thatís the same route I would go to test. I just followed your testing in the thread so you could go back over everything. There shouldnít be anything else to check besides swapping to another breaker in panel. Once you disconnect the element that will tell us where the issue is. We donít replace a lot of the relays. We have them if needed.
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Old 11-24-2022, 03:04 PM   #5
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Is the coolant so old and contaminated that it has become conductive? The original solid state relays were garbage and burn up. I smelled burning plastic several times in my kitchen and could not locate it over a month long period. Then the magic smoke got out. It was cheap to replace the element, snap discs, and relay all at once. Rebuilt the blower motor at the same time. Been trouble free since. Also check the wires at the breaker and at the aquahot entrance box for being tight.
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Old 11-25-2022, 12:18 PM   #6
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Root Cause...

Quote:
Originally Posted by Bobby Dowdle View Post
.. Once you disconnect the element that will tell us where the issue is. We donít replace a lot of the relays. We have them if needed.
So first I lifted the neutral leg, thus creating an open circuit downstream of the heating element. Breaker tripped immediately as before. Next I went to disconnect the heating element from its upstream neighbor the AC high temperature limit switch. As I was removing the wire from the heating element, it basically came off in my hand. The break was at the spade terminal on the limit switch.
Funny that it would read acceptable resistance to ground (was about 2K ohms so not a dead short) but fail when energized. At least it's a cheap replacement part.


It looks like I can unscrew the limit switch / thermostat without having to do a fill & drain procedure. Is that correct?
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Old 11-25-2022, 12:23 PM   #7
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...Is the coolant so old and contaminated that it has become conductive? ....
Any coolant being 50% water will be conductive, won't it? I believe the heating element itself is electrically isolated from the coolant by the outer tube of the element. Pretty sure that the internal filament is what gets the juice and heats the outer tube which transfers the heat into the surrounding coolant / water.
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Old 11-25-2022, 06:10 PM   #8
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Quote:
Originally Posted by markpj23 View Post
So first I lifted the neutral leg, thus creating an open circuit downstream of the heating element. Breaker tripped immediately as before. Next I went to disconnect the heating element from its upstream neighbor the AC high temperature limit switch. As I was removing the wire from the heating element, it basically came off in my hand. The break was at the spade terminal on the limit switch.
Funny that it would read acceptable resistance to ground (was about 2K ohms so not a dead short) but fail when energized. At least it's a cheap replacement part.


It looks like I can unscrew the limit switch / thermostat without having to do a fill & drain procedure. Is that correct?
Remember your ohm meter is pushing just a few milliamps through the wiring. It's not reading a resistance like in the case of an almost broken wire that tries to carry 15 amps. Any of the screwed in tank items can be changed without draining. A few rags below and move fast. The fact it's a sealed system so to speak keeps the coolant from pouring out to a large degree.
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Old 11-30-2022, 08:00 AM   #9
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tripping

Hello I was just wondering if your breaker is faulty. Just a thought. Thanks
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Old 12-04-2022, 06:37 AM   #10
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Resolved!

Had to wait a week for the new AC high temp limit switch to arrive. Was a pretty easy swap but space is tight. Turns out the limit switch can be removed with no loss of boiler fluid. I did check the fluid level by removing the tank cap and it was right at the bottom of the filler neck as it should be.

Glad I diagnosed and did the repairs myself. Learned a LOT about the system and spent only time and $18.
Thanks to all who provided guidance. Love the support here on this forum!
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