Aquahot Preheating Without Permission

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Aquahot Preheating Without Permission

February 24, 2014, 06:30:39 pm

I was wondering if anyone has seen this before. While looking at the various systems of our coach I noticed that the engine coolant INPUT line to the aquahot is warm. We are running the 115v aquahot setting all of the time for domestic hot water. At the time I didn't think much of it but I realized today while working on the engine that the block and coolant lines near the block were fairly warm. I traced it all the way to that engine out -> aquahot in line and it was hot! The engine preheat switch is off. If I turn engine preheat on the COLD output line gets hot as you'd expect. It seems like as the system sits off and hot, convection is causing reverse coolant flow and causing the engine to heat. I imagine this is where our $200 electric bill came from.

Any ideas? I don't see any check valves in the engine preheat loop in the parts list. I'm tempted to just put a cable actuated 3/4 valve in near the aquahot, close it and be done with it.

Re: Aquahot Preheating Without Permission

Reply #1 – May 23, 2015, 08:44:50 am

I have noticed the same issue on & off for the last year. I'm convinced that this is something that has occurred periodically throughout the life of the coach. I'm considering a manual or electric valve located at the engine. Did you find an answer?

Re: Aquahot Preheating Without Permission

Reply #2 – May 23, 2015, 09:37:33 am

Bob,

Engine coolant circulates through the Aqua Hot heater when the engine is running and when the engine preheat pump, located in the heater is on. With both of those off, heat would have to transfer via convection. A cut off valve would stop that.

With valve closed, no heat from the engine when traveling down the road which is not a problem. And if left closed, turning on the engine preheat pump would cause the pump to pump against a closed loop. Tough on the pump.

First time I have heard of heat convection causing excessive or any use of electric heating element. But I am not saying that is impossible just the first time. I am concerned that this is the problem because thousands of other heaters are not having this situation.

I would encourage you to ask this question over on the Aqua Hot Forum. All the best.

Re: Aquahot Preheating Without Permission

Reply #3 – May 23, 2015, 12:07:30 pm

Rudy,

I think this is more common than realized. The first time I found the engine hot I was sure that the preheat pump was running. That was not the case. I had a discussion with AquaHot tech support before posting this issue and was told that the way Foretravel plumbed the system was not at the preferred locations on the engine.

Re: Aquahot Preheating Without Permission

Reply #4 – May 23, 2015, 03:26:15 pm

I wonder if both IN and OUT lines on the AH could be routed down to create a thermal trap?

Re: Aquahot Preheating Without Permission

Reply #5 – May 23, 2015, 05:12:57 pm

Seems that 12-v solenoids that are normally closed would prevent any engine coolant line circulation when engine pre-heat pump is off. Connecting solenoid power to the wire that is powered when circulation pump would open the lines when needed. You could also open solenoids when ignition is on via diodes to keep the ignition power from running circulation pump.

If there is no shutoff built in, it seems that everyone would have this situation when parked.

Re: Aquahot Preheating Without Permission

Reply #6 – May 23, 2015, 09:10:42 pm

Bob,

Thanks for the additional info. I will see what I can find from the folks I chat with.

Re: Aquahot Preheating Without Permission

Reply #7 – May 24, 2015, 06:18:09 am

Rudy,

Is it possible that this condition is affected by the coach level position? We at a site that is beyond the ability of the system to achieve bubble level, with the front slightly lower than the rear. The hoses from the AquaHot are going uphill. This might explain the intermittent nature of this problem.

Re: Aquahot Preheating Without Permission

Reply #8 – May 24, 2015, 07:48:25 am

Bob,

Your are the first time for me on this issue. So Tuesday, I will be asking around to see what I can learn about heating the engine with preheat off and the pump not on by some electrical problem. Thanks for adding you are stern low.

Re: Aquahot Preheating Without Permission

Reply #9 – May 24, 2015, 08:11:54 am

I wonder if you took a reading of the temp in the engine area now and then turn the pump on and see how much if any it increase would help in diagnosing it.

Re: Aquahot Preheating Without Permission

Reply #10 – May 24, 2015, 08:33:44 am

Sure would be nice to know the pump is indeed off. A failed switch stuck on would explain his situation.

My first concern is you guys do not have this happening to you all and he does. So what is different in his case?

Re: Aquahot Preheating Without Permission

Reply #11 – May 24, 2015, 09:04:29 am

Bob,

Have you disassembled the circulation pump to see if you have had a impeller failure? If impeller has broken a vein it may be passing antifreeze and not sealing off.

@ Rudy, Have you ever seen a failure of an impeller though?

Pamela & Mike

Re: Aquahot Preheating Without Permission

Reply #12 – May 24, 2015, 09:27:24 am

Mike,

The pumps in his heater are some of the most robust AH has used. They rarely fail and when they do it is mostly a leaking O-ring but still working fine.

I am not sure how much an impeller shuts off fluid flow since with the preheat pump off, the main engine coolant pump moves coolant through the heater allowing heating of the coach while traveling down to about 50 degrees F.

Wish he was close to me as I would sure like to look this one over to see what I could discover. There is a reason for this situation, just need to find what it is.

Re: Aquahot Preheating Without Permission

Reply #13 – May 24, 2015, 09:36:59 am

The engine preheat pump is Definitely off. The coolant from the AquaHot, at the inlet of the engine water pump is 89ºF. Coolant out of the block is 75ºF. Outside air temp is 61ºF.

Perhaps piku can jump in and let us know if he still has the same issue.

Re: Aquahot Preheating Without Permission

Reply #14 – May 24, 2015, 09:44:39 am

I disassembled one of the circulating pump motors a while back to reinstall the rear motor plug that had fallen in. I seem to recall that the pump assembly is not directly coupled to the pump shaft, instead is magnetically driven. This configuration eliminates the need for a shaft seal and potential leaks. This is not a positive displacement pump and will not seal off.

Re: Aquahot Preheating Without Permission

Reply #15 – May 24, 2015, 11:59:53 am

Dave,

Both of the heaters you have had did not have a shut off valve so you always had/have engine heat transfer to the heater coolant when driving.

Now an installed cutoff valve turned off would stop engine heating when traveling. Would stop engine preheat unless turned back on.

Bob,

Again thanks for the addition info. With the pump off, I can only think convection is the source of the temp at the engine. I do know the copper pipes at the tank under the burner are always hot from convection.

Re: Aquahot Preheating Without Permission

Reply #16 – May 24, 2015, 12:09:12 pm

The in-line ball valve to engine would be a good idea while in storage or while camped in one location for a length of time (particularly if you are paying for electricity).

Yes, it would have to be left open other times. And, if there is a separate circulation pump for that circuit, the valve would have to be open or you would likely burn up the pump so a second switch just before the pump would be a good idea (consider it the fail-safe switch).

Really depends on how you use the coach.

Re: Aquahot Preheating Without Permission

Reply #17 – May 24, 2015, 08:30:13 pm

Bob,

Drop by a tool store and pick up a 20 dollar hose pinch plier. Get the kind that look like vise grip plier.

Pinch one of the engine hoses and see if your problem goes away. Pinch it tight.

Re: Aquahot Preheating Without Permission

Reply #18 – May 24, 2015, 09:32:44 pm

Rudy,

I pinched off the supply to the engine this morning. The engine is cold.

Re: Aquahot Preheating Without Permission

Reply #19 – May 24, 2015, 09:52:48 pm

Bob,

If I learn more on why you are getting so much convection heating, I will let you know. Thanks for the learning experience for myself.

Re: Aquahot Preheating Without Permission

Reply #20 – May 24, 2015, 10:41:55 pm

A ball valve or solenoid would solve the issue.

Re: Aquahot Preheating Without Permission

Reply #21 – May 26, 2015, 12:49:59 am

Sorry Bob, I forgot to call you. We have a ball valve we installed on the heater hose coming out of the water pump area. It solves the issue quite effectively and doesn't seem to harm anything if you forget to open it up when you drive. We've had a busy couple weeks making plans for and moving from FL to PA.

Re: Aquahot Preheating Without Permission

Reply #22 – May 26, 2015, 04:44:30 am

piku,

Thanks for the response. I'm probably going to do the same thing when I get a chance.

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