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Aquahot Expectations - What's Reasonable?


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This is a question for the folks actually using an Aquahot 400D for comfort heating.


We're relatively new coach owners. Our coach uses an Aquahot 400D unit for comfort heating and hot water. We've never had any problems with hot water. However, the heat functions have been an issue since we first took possession of the coach.


Initially, we were experiencing a problem where during periods of cold (i.e., ambient outdoor temps in the low 30 - high 20 degree range) the heat exchangers located inside the coach simply would not come on. Once the ambient outdoor temps rose to the high 30's, low 40's ... the problem went away and the heat exchangers immediately kicked on. If/when the ambient outdoor temps fell again - the problem returned. The folks at the RvHydronicHeatRepair.com suggested that problem was an issue of the Aquahot not getting hot enough for the "Low Temp Cutoff Switch" to allow the heated boiler antifreeze to circulate out to the heat exchangers. It sounded as though it's a common problem (especially for coaches are "winterized" on the fresh water side of things. The suggested "work around" was to simply bypass the "Low Temp Cutoff Switch" when the coach is "winterized". I confirmed that recommendation with the folks at the Aquahot support line itself - and have now bypassed the "low temp cutoff switch". Now, the heat exchangers come on whenever the thermostat calls for heat. I can hear the fans and feel the heat.


Despite knowing that the system is heating the boiler and delivering heat to the heat exchangers in the coach - the system still doesn't do much in terms heating up the coach. Planning to doing some prep work in the coach late yesterday afternoon in anticipation of an upcoming trip to Florida - I stopped by the coach yesterday morning and fired up the AquaHot (running on diesel fuel) in the hopes of heating the coach so that it would be warm when I returned to do the work I had planned. The ambient outdoor temp was hovering right around 30 degrees - and the thermostat inside the coach read 37 degrees. When I left - the Aquahot was running, the heat exchangers were getting warm and the heat exchanger fans were running. When I returned 4+ hours later - the temperature inside the coach had only risen to 45 degrees. Upon my return the heat exchangers were definitely warm - and the heat exchanger fans were running.


Being that I've obviously got heat being generated by the boiler as well as being delivered to working heat exchangers. I'm starting to wonder if the Aquahot solution simply doesn't have the heating capacity to heat the coach in cold​ weather.


This brings me to my question. I'm trying to decide whether I've got a broken system ... or whether I've simply got unrealistic expectations regarding what an Aquahot can deliver. What sort of experience are other Aquahot users having when trying to heat their coaches in cold (high 20 - low 30 degree) weather?

The Spacenorman

2012 Holiday Rambler Endeavor 43' DFT

2012 Jeep Liberty

Our Travel Website: www.penquinhead.com​

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I know many with Aquahot systems that brag how comfortable they are in freezing weather, so I would go with the idea you have a broken system.

2004 40' Newmar Dutch Star DP towing an AWD 2020 Ford Escape Hybrid, Fulltimer July 2003 to October 2018, Parttimer now.
Travels through much of 2013 - http://www.sacnoth.com - Bill, Diane and Evita (the cat)

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Why don't you call the manufacturer. You should use an infrared heat gun to detect the temperatures coming out of the radiators. That way you have some info for the manufacturer.


Your system is clearly not working well. While the propane Aquahot does have some btu limitations that make it "not optimal" for coaches in the 45' category, your diesel fired unit should easily heat the coach if installed properly and performing properly. Assuming that it is installed right I'd say you have an issue.

Jack & Danielle Mayer #60376 Lifetime Member
Living on the road since 2000

PLEASE no PM's. Email me. jackdanmayer AT gmail
2016 DRV Houston 44' 5er (we still have it)
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You need to call Aquahot. They will talk you or a repair person through the problem.

It sounds as though the check valve on the circulating system is not opening, stuck partway open or the pump is not functioning properly.

There could be something else wrong but they will figure it out.

On occasion there is some oddball thing wrong. I have seen where pet hair has restricted the air flow on a heat exchanger. previous owner had a dog that apparently shed.

I am an authorized dealer located at the North Ranch in Congress Az for the winter.



safe Travels, vern

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You have a system problem. I, too, have been prepping the coach. 30F as a high today. Coach at 60F inside which is the thermostat setting when I was working inside. Increased 10F in less than 20 mins.

A good stocking stuffer is a remote temperature gun. Got mine at Radio Shack for under $20. Your piping temperature should be at 180F on shutdown of burner. Burner on at 165F. Exhaust pipe temp in the 250F range and no smoke.


Good luck,


Bill & Lynn Baxter

MCI102A3 Conversion, Detroit Diesel S50  


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It appears that the "Control Thermostat" - which the manual says "is installed into the Aqua-Hot’s boiler tank and monitors the temperature of the antifreeze and water heating solution to determine when it is at operating temperature and when it requires heat. The Aqua-Hot is considered to be at operating temperature between 158°F and 190°F." is apparently wonky. According to a local dealership - it wasn't allowing the boiler to heat up past 125°F.


The necessary parts order was been placed at the end of the day yesterday - however, with much of the industry taking time off during the holidays (the huge dealership I took it to is actually shut down between Christmas Eve and January 4th?!?!) - I been told that the coach likely won't be ready to be picked up until January 5th.


I'm viewing this as good news on two fronts - first, something has actually been diagnosed as faulty (which means there's a likely fix!!) and second, because it sounds like it will be fixed with a couple of days to spare so it won't impact our planned departure for Florida!

The Spacenorman

2012 Holiday Rambler Endeavor 43' DFT

2012 Jeep Liberty

Our Travel Website: www.penquinhead.com​

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