Aqua Hot Aquastat Failures

[Dick Simonis]

I' curious as to why the high limit aquastats seem to have a short life span.

When I bought the coach in Sept last year the AC heater high limit was bad and BCS replaced it.  Last month it failed again and I purchased a new one from Hydro Hot  for $39.  Twp weeks later the 12 VDC one failed and that one cost ~$69.00.

What give with these things and does anyone have a clue as to why the 12 VDC aquastats are so much more expensive?

Guess I need to keep a spare of each at this rate.

Thanks for any insight.

Dick

[Edward Buker]

Dick,

My guess is that the 120V Aquastat PNs are built in larger volumes having more applications than the 12V ones. Technically they are not that different, the 12V may have bigger contacts to handle more current. Each make and break produces an arc which erodes and pits the contacts so they have a life and they are in a hot environment. If it is a short life then the metals being used are not up to the task favoring cheaper manufacturing costs. Gold contacts would pretty much last forever, so we know they are not gold....

Later Ed

[Orman Claxton]

Dick, What's  your model #
I have not experienced that problem, is your coolant level full?
does your Tstats have full contact with the mounting surfaces?
Do you have full Voltage?
 

[Dick Simonis]

Omar, I have the AH$E-100-2S.

Yes the tank is full of coolant and, as far as I know, they have full contact.

[Orman Claxton]

Dick are you using the proper t stats in the proper location?

[Dick Simonis]

Omar, yep they seem to be correct.  Also, I just remembered I had to replace the AC high limit in March also so they have now been replaced 3 time in one year.

It's a rainy and cold day today (I'm now in Stoneridge, ID) so I think perhaps a call to Aqua Hot may be in order.  The unit is working great in the mid to high 30 degree nights so I'm pleased that at least.

[Edward Buker]

Dick,

Check your readout panel what the AC current is with the heating element breaker on and off while calling for heat. I am assuming it is working which may be incorrect. If not you can jumper the bad Aquastat for a couple of minutes to get a reading. There is some chance that a higher wattage element was put in at some point and may be pulling more current then the Aquastat is designed for. Should be 1500W which is just over 12 amps.

If that is correct I would buy your next Aquastat replacement from a different source in case there was a defective run of them. The AC high limit is made to open under an overheat condition, so the contacts should not be make and break stressed normally unless the lower temp Aquastat was failing and not opening its contacts. In that case the high limit one is always opening and closing and acting as the limit switch which would cause it to fail. I would replace both of those Aquastat units as a pair this time and use a little thermal conducting grease between the cap and the tank on both Aquastats so physically they are touching the tank and grease is filling the gap. That assures the Aquastat cannot get hotter then the tank itself which could happen with contact resistive losses.
If you do this I do not think you will continue to have an issue. This is the thermal grease I recommend given its high temp capability. I have the same unit and have replaced mine and have had no issue in the last 4 years. Hope this helps.

http://www.amazon.com/Super-Lube-98003-Silicone-White/dp/B0044NI2M2/ref=sr_1_3?ie=UTF8&qid=1442504852&sr=8-3&keywords=thermal+compound+automotive

Later Ed

[Dick Simonis]

OK, called Aqua Hot and was told there are only two ways the high limit can fail.  Low coolant and a bad control Aquastat.  Since I know the coolant is not and has not been low that only leaves the control Aquastat that can cause my issue.  His recommendation is to replace both control units.

He also confirmed that the high limit control does NOT a reset so it acts more like a fuse in that regards.

Also, the control Aquastat can easily have an intermittent issue so they might work fine and only occasionally not open.