Failures in a Aquahot 450D apparently caused by low coolant

[jaysigel]

While camping in the DC area, the electric element on our Aquahot 450D failed to come on. The Aquahot (AH) is in a 2022 Foretravel FS450. We turn it on via the Silver Leaf panel and can monitor its power draw via the Victron Cerbo-GX panel. It showed no power draw from the 1650 watt element. The diesel still worked for 2 more days, then that stopped. The Reporter touch pad above the AH unit lets you diagnose, test and reset faults. The Reporter showed a high temperature fault. The reservoir was empty and and I topped it off with Century coolant. (Prior to embarking on the trip, the reservoir was adequately full.) There was a wet spot on the gravel under the AH unit, but there were no signs of leakage, either on or inside the unit, nor in its bay. After refilling the reservoir, the diesel burner would not fire.


I had a Hydrohot 250 unit in our old coach for 19 years and did all of its maintenance and repairs myself. The 450D is more sophisticated but similar. I was not in a position to service the unit in the campground and so we used the campground's showers. We purchased this lightly used coach last year and I had not serviced the AH before.


While pondering what could be the problem, I assumed that the electric element had burned out. I ordered a new one plus a thermostat before heading back home, both relatively inexpensive. I sent multiple inquiries to HeatMyRV.com and Aquahot.com and never got any responses. While driving, we got hot water off of the engine, the so-called Aquahot "motor-aide" function. After driving 500 miles and at the next campground, the reservoir tank was again empty. This time, I didn't have enough coolant to refill it.


Back home, the AH parts arrived. The contacts on the electric element are awkward to access inside the 120V "dog house" and the multimeter showed it to be open. To remove the element, the coolant has to be drained. I filled up a 4 gallon bucket and then stopped draining. The system is supposed to hold 5 gallons. Once the element was removed, it read 8.7 ohms, meaning that there was nothing wrong with it. There is a thermostat right above the element and it has a reset button in its center. I pushed the button back in. Then, I noticed that the 2 other thermostats near the burner also needed to be reset. They prevented the burner from igniting.


The refill method on the AH, per the service manual, says that it needs to be refilled via a pump attached to the drain hose, not via the reservoir. That required getting a garden hose to 1/2" NPT adapter that screws into the drain line ball valve. By coincidence, I also happened to have a small sump pump that we used to drain a blow-up kiddie pool during the pandemic. It discharges via a garden hose connection. Using it, I pumped back the coolant after replacing the electric element. Then, the Reporter read that the tank was full. I placed about a gallon of new coolant into the reservoir. I purged the 5 pumps as instructed and some bubbles briefly entered the reservoir but the reservoir level didn't change. The Reporter again indicated that the tank needed to be filled. I added another gallon to the bucket and pumped that into the drain line until the reservoir level increased. I repurged the 5 pumps but there were no air bubbles.


The AH won't heat up with the cover off for safety reasons, but with the cover back on, the diesel fired up and turned off at 197 degrees. After it cooled, I tested the electric element and it worked normally, heating the coolant to 176 degrees, shutting off and then coming back on after using some hot water. During the heating tests, the reservoir fluid level would go up a little towards the hot marker line and then decrease a little as it cooled, which is as it should. The manual says that in order to find leaks, the unit needs to be brought up to operating temperature. There were no visible leaks. Overnight with the unit off, the reservoir level hasn't changed. There is no wet spot under the unit and everything is dry.


Thinking about what actually happened, it appears that the AH coolant tank is a closed but non-pressurized system. As the coolant evaporates, it should get refilled from the reservoir, which acts like a water seal. If the tank level falls enough to pull all of the available reservoir fluid into the coolant tank, the resulting air on top the coolant tank will make it difficult to add coolant to the system via the reservoir. In that case, it appears that the only way to refill the tank would be via a pump into the drain line. Most users will not have the hose adapter or fluid pump. Coolant = boiler antifreeze is expensive at over $40/gallon. You cannot use RV/marine or automotive antifreeze.


You don't know the status of your AH 450D system unless you query the Reporter inside the AH's bay. Our coach has RV-C, but the Reporter doesn't communicate with the Silver Leaf. A low coolant situation will mimic failures of various other AH components.

[Chap1021]

You don't mention the coach you are driving. Sounds like your control thermostat is controlling high. Also when driving the aquahot can heat up with engine heat.


The control thermostat should shut off the electric and the diesel burner at 185 degrees. There are three high limit thermostats are 215 degrees. You said it got up to 197, that is high. My control thermostat stuck on and the aquahot belched out several gallons of antifreeze until the high temp thermostats took it out at 215. We had no hot water the next morning, a big wet spot on the ground and a low level in the aquahot. After changing the control thermostat, resetting the three high temp thermostats (two on the diesel control and one on the electric element), and refilling, the system worked fine.


At high altitudes and low barometric pressure you can lose more fluid due to evaporation. I was in Albuquerque when the thermostat stuck and boil over happened to me. Also the engine will put more heat into the aquahot when it is working hard. The 605HP will put more heat into the aquahot than the 450HP.



There is a ball valve on the engine you can manually shut off the engine antifreeze loop to the aquahot and I have closed that in warm weather to limit the heat going into the aquahot and the amount of boil over. I used my awning hook to pull the handle open or closed in the engine compartment as it is hard to reach.
When driving during cooler weather and heat is required, on the Firefly, turn the aquahot electric and diesel burners off. Turn on the aquahot to the zones, including the basement. Turn on the floor heat and turn up the thermostats. I turn them up higher than normal. The aquahot provides engine heat to the coach while driving down the road. You have a nice warm coach when you arrive using the heat off the motor while driving. Also the amount of aquahot boil over is reduced because the heating zones are on.


Also you can get a refractometer and measure the antifreeze concentration. As it gets over concentrated distilled water can be added. The recommended mixture is 30-50% poly glycol. Over 70% the freezing point actually increases. At 50/50 the boiling point is 222 deg, so it is close to the 215 high temp limit thermostat. The refractometer can also be used to check def and the main engine antifreeze.

[jaysigel]

Thank you for your response.

Actually, our coach type is listed in the 2nd sentence. It's a Foretravel FS450 2022 (the little Realm, no longer manufactured). It has Silver Leaf, not Firefly. There is no separate basement heat setting. Zones are floor, front and back. We have only used the heat pumps for interior heating and cooling.

We've only owned the coach for only a year. In retrospect, I was surprised how well the electric element heat was working (before it failed) compared to its function in the Hydrohot in our prior coach (a 38' 2006 Travel Supreme DP that we subsequently sold). That tends to support a control thermostat failure.

The AH shouldn't overheat. A replacement ETS module (control thermostat) is supposed to arrive today or tomorrow. A 10 mm deep socket is also arriving, supposed to be required to remove the module per the service manual. I'll check the specific gravities with 1.040 supposedly being ideal from what I've read. I also placed an order for a 5-gallon jug of boiler antifreeze from Home Depot. When the AH failed, the engine was our only source of hot water and we could then have enough hot water for a hot shower shortly after arrival! Our HydroHot never overheated and had the same Motor-Aide connection to the engine. I had left the shut-off valve open so that upon arrival, we would have hot water to wash the accumulated dishes from breakfast and lunch without having to wait for the AH to heat up, but perhaps,as you suggest, that's not a good idea.

More concerning is the lack of response from AquaHot for technical support. I am very disappointed with them.

[jaysigel]

Page 7 of the AH service manual shows the Operational Flow Chart, which says that the boiler tank is heated to 190 degrees. The Reporter on our AH read that the coolant temperature was 196 degrees at which point the burner shut off. With that being less than 3% above the 190 degrees, it suggests to me that the temperature control module is probably working properly. That leaves 2 unanswered questions:


Did the unit overheat because the coolant level was low?
Did the coolant level get low because it overheated?

[Chap1021]

Normally the engine loop valve is always open. I shut off the engine loop to the aquahot if I am taking a trip where I knew the engine would be working hard and I did not need the heat in the coach. This would limit aquahot fluid loss. The second reason is if there was a leak in the engine loop.

[Chap1021]

Aquahot must list the temperature of the controlling thermostat different in different places. In my parts manual it says 185 degrees.

[jaysigel]

I have the latest versions of the 450-DE5 service and parts manuals. I did a search for every place that the word "temperature" occurs in both manuals. (I can't do a search on the degrees symbol because it is not a computer keyboard character.) On page 7, the flowchart shows the temperature of 190 degrees. On pages 14 and 16, the illustrations of the Reporter readouts show the same 190 degrees. Nowhere does it say at what temperature the burner or electric element shut off. The flow chart does show that the heating zones require at least 150 degrees for the pumps to be activated. The thermostats do trip at 215. A search for 185 showed nothing. Please reference which manual, which version and on which page has 185.

On page 16, the replacement procedure for the ETS module is incorrect. I received a new module 2 days ago. The instructions call for using a 10 mm deep socket. The wires are permanently attached to the module. Only a 14 mm socket or wrench will fit on it, not a 10, and a slot socket will be the most practical (like those used for wing nuts) to remove and reinstall it without cutting off or damaging the wires.


I'll go further. The Century coolant sold by AquaHot with AquaHot's own name on the label says do not dilute, ready to use. AquaHot's own specifications call for using a "50/50 mixture" of propylene glycol. Right out of the container, the specific gravity tests less than 1.030 and that equates to 35%. I tested the coolant specific gravity in my unit via its drain line and it measured the same specific gravity. AquaHot's Century coolant container does not list anything as to its contents other than propylene glycol and it being "GRAS." I bought 5 gallons of Cryo-Tech 100 at Home Depot yesterday. It, too, is designated for hydronic heating systems (it cost less than $200 with tax, the best price that I've found). It has beaucoup specifications on its container including a listed specific gravity of 1.054. It appears that AquaHot is selling their so-called 50/50 coolant, which is actually 35%.


And they still haven't called me back.

[Chap1021]

Aquahot lists it different in different places. It is listed as 185 in manual "450-DE2 Service Manual Rev C" on page 72. It is also listed as 185 in a parts manual, but it is not worth looking up. Needless to say, Aquahot has changed the the setting unless they just stated it incorrectly in several places. The actual thermostat part has been superseded in newer models and that may have been when the setting changed. You have a newer one so go with 190, it is not that big a deal.

[jaysigel]

Aqua-Hot 450-DE5-Parts-Manual page 5.pdf



Aqua-Hot 450-DE5-Service-Manual-11.14.23 page 18.pdfI did get an email back from AquaHot who said, tersely, "It's probably the thermie," and he asked for my AquaHot's serial number, which I had given him previously.


Next, I put in a phone call to AquaHot and they actually called me back later that afternoon. She said that it was probably the temperature module (thermistor). I explained:
1) Incorrect instructions for its removal, requiring a 14, not a 10 mm socket and the socket needs to have side slots because the wires don't come off.
2) Incorrect listed part number in the parts manual (it doesn't end in 711 but in 712, there being no such part 711)
3) Absence of any parameters at which the Reporter should be expected to turn off the burner or electric element
4) The Century AquaHot coolant not being the required 50/50 propylene glycol concentration (it's 35%)
5) The telephone and website advice to send emails to service@aquahot.com, which is not a real email address (everything bounces back) and that the correct email address is servicedept@aquahot.com


Replacing the thermistor is a quick and easy job if you have the right tools. First, you need to drain out about 2 gallons of coolant and figure out how you'll get it back in. Next, you need locate the thermistor, which is located on the left side of the burner, below and between the 2 burner thermostats. Next you disconnect the 2 spade plugs on the end of the wires. Using a 14 mm wing nut socket as shown in the attached picture, you remove the thermistor. After removing it, you insert the new one carefully by hand to make sure it is not cross-threaded before tightening it up. Then you put back the 2 gallons. I used a sump pump to push it back into the drain line.


Afterwards, I tested the new thermistor - same as the old one. The burner fired up and cycled off at 190 degrees. As the blower keep running for a few minutes, the temperature continued to rise to 186 degrees, the same as before. Did I really accomplish anything?