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Aquahot blowing cold air after blowing hot air for 10-15 minutes


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Hi everyone I have a new aquahot problem. I have an 02 Executive 40PBT with the the aquahot model #AHE-100-02s. The zone 2 heat exchangers ( bedroom and bathroom) have been working great this winter until Friday. Friday night they started to blow cold air after about 10-15 minutes of blowing hot air. Monitoring the system the last couple of days it seems hot air will come out of the exchangers for a little bit longer while the burner is ignited. But I still get cold air coming out (after initially getting hot air) after about 15 minutes. Usually (from my experience with my coaches unit) the aquahot system will reach full temperature and automatically turn off after about 20 minutes. It seems that I can still get hot air from the exchangers/vents for about 10/15 minutes with the AH switch in the off position if the antifreeze is still hot from a previous heating of the AH system. My previous problem with low air flow in zone 1 has not been solved properly. My guess is the fans are not getting enough electricity, the wire guage is so small I am afraid to touch them for fear of breaking the wire strands inside the insulation. I am using a temporary fix - an Olympian wave 8 propane heater in the front of my coach. Expecting snow tonight and most days over the next week, not going to be as cold as it was in most of December, low 20’s most nights and mornings, the coldest night/ morning was 17*. Thanks for the help, I read the older posts that I could find in the archives but nothing seemed to be similar to what I have going on 

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I had the same problem 3weeks ago. My front zone was working fine on me 05 sig and then started to blow cold air. I would low cold each time the front zone called for heat. My other 2 zones worked fine and heated well.

I pulled the cover off and found a thin power wire to the pump was corroded through at the connection. A new spade connection and every started working again. I did clean the other 3 pumps connections and all is good for now. Good luck.


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Just some thoughts.  The AquaHot system is really very basic, as complicated as it looks.  But there aren't very many potential failure points.

If you are getting heat for a time, the burner and/or 120 VAC sources for heating the unit are probably working.  You can easily check to see if you are actually running it out of heat in the reservoir by waiting until the exchanger is blowing cool air and then turning on a hot water tap and see if you have warm or hot water available.  That will determine very quickly whether the problem is with the heating loop or with the main unit.

If you have hot water at the tap and/or the other registers, the problem is either with the operation of the fluid loop or with the fan in the heat exchanger.  You are saying it "started to blow cold air".  If it is indeed blowing, your problem is probably not with the heat exchanger, but rather with the fluid loop.  If it is not actually blowing air, the fan is probably the issue, and that could be with the fan itself, the wiring between it and the AquaHot or the AquaHot control board, itself.

By the way, there are a number on LED's on the control panel of the AquaHot on the AHE-100's that will tell you what is running and what is not.  They are not numbered intuitively.  For example, on our '06 Dynasty, the bedroom is zone #1 and it is operated by pump #1.  The bathroom is zone #2 and is operated by pump #2.  The basement is actually zone #3, but it shares pump #2 with zone #2.  Zone #4 is a spare zone.  The front main part of the coach is zone #5 and is operated by pump #3.  Then there is also the engine pre-heat zone which is the fourth pump you will find in the enclosure, probably mounted below the other three and on a different axis.

So the questions are: 1) Is the fan actually running on the heat exchanger in question?  2) Is the "coolant" in the AquaHot getting hot and/or staying hot?  3) Is the appropriate pump getting power when you observe the problem? (Check the LED on the panel).

Potential failure points: 1) AquaHot reservoir having sufficient hot water to do the job.  2) Zone circulating pump actually circulating the "coolant" when the heat is being called for.  3) The check valve in the line coming out of the top of the unit for that zone opening and staying open.  4) The fan is actually operating at the heat exchanger.

If you check those things out and you still have the problem, here's a link to the service manual for that unit.

http://www.aquahot.com/files/service_manual/AHE-100-02S Service Manual Rev. B 9-27-2011.pdf 

Let us know how you make out.

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Guest Ray Davis

If it is only zone 2 that is affected then it appears that zone 2 pump is at fault.   There is a check valve in each zone that is problematic but I have never heard of one          causing your issue.   The check valve usually sticks and doesn't allow heat from the beginning, until it is jarred open.

You can usually take the cover off and tell by feel if each zone pump is running and if each pipe is hot.

Roger Berke has a great site and forum where you can get help.


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SUCCESS!!! It was a good feeling this morning when I got up and had your 3 responses to my post. I have both the shop manual and the owners manual. I started looking around this afternoon and first found a loose nut that holds a bunch of positive wires. Tightening that didn’t solve the problem. I then checked all the fuses, they were all good and they had a fresh coat of dielectric compound on them. I had the AQ system serviced during the summer of 2019.  There were a couple of problems 1) 2 of the relay sockets were bad and 2) the fuel pump was leaking. Both of those issues were fixed, everything worked well when I brought it home. I had it in storage until spring of 2020 and didn’t start using the AQ system until winter of 2020. On my way out of that tight crawl space after checking the fuses I knocked all 3 relays out of their sockets. After putting them back in I now have zones 1 (A) and 2 (B) working properly. So the problem stemmed from the relays not having a good connection.” Thanks for the advice. I haven’t figured out where zone C is. It is not the bedroom as the manual states, it seems both the bedroom and bathroom exchangers work off of zone 2 (B). It may be the fresh water tank/ bay pump but the check valve is not getting hot with the bay fan working. So now my zone 1 (A) fans are stronger than my zone 2 (B) bedroom and bathroom fans a reversal of what I had before. I will be warm tonight, thank you again

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