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Old 11-01-2021, 07:04 PM   #1
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Hydro Hot issues

We have an 06 Intrigue that has a Hydro Hot hydronic system that has been a seemingly constant source of frustration ever since we bought the coach 2.5 years ago. At least 4 different techs have worked on this system, including John Carrillo (Heat my RV), Howards RV (San Bernadino), Premier RV (Oregon), and RV Repairmen (Colorado). All are certified Aqua Hot techs. Each repair session has been expensive (total in excess of $4K) and has not solved the recurring problems. I have had the unit serviced regularly.

We appear to have two issues: 1. Constantly losing coolant somewhere resulting in a low coolant level warning resulting in a refusal to start up. and 2. The unit will not pull any coolant from the overflow/reservoir tank. The different techs have performed complete flushes twice, replaced the float level sensor twice, replaced the tube and clamps to the overflow/reservoir tank twice, replaced the radiator cap and checked all of the fittings for leaks. The last repair included replacing the control board and some internal parts including a stainless cylinder that has some function in the burn chamber. The old cylinder had a small crack and carbon deposits.

To my knowledge, during the drain and flush procedures, no pressure test was done. I always watch carefully for leaks that appear on the ground or around the unit and there have been none. After talking with tech support at Aqua Hot, they suggested putting a dry paper towel on top of the radiator cap which would result in a damp towel if the cap was leaking. After 3 days of use the paper towel was dry.

We recently took a 4 day shakedown cruise before heading south for the winter. The first night the HH provided heat and hot water, but by morning would no longer fire up. Sure enough the low coolant light was on. The reservoir was 2/3 full and at the correct level. Removing the radiator cap, I could not see or feel any coolant in the tank. I poured nearly a gallon of coolant into the tank before it filled to the neck. Replacing the cap and checking that it was fully tight, the unit performed perfectly for the next three nights. The next morning, I checked the unit and the low coolant light was on again. Again the reservoir had the same level but the tank was very low, as I added 3 quarts to fill it to the neck again.

No visible leaks anywhere, the cap is not letting steam escape, where is all this coolant going? If you haven't bought any boiler antifreeze lately it is nearly $40 a gallon.

If anyone has had a similar problem or has any ideas, I would love to hear about them. Aqua Hot says a replacement unit runs nearly $9K before installation costs. All responses are very much appreciated!
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Old 11-01-2021, 08:40 PM   #2
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I believe you have a leak in the heat exchanger and your coolant is just getting into your fresh hot water lines. Two things lead me to this belief:



1. No change in overflow / expansion tank level. The thing that draws the fluid from the expansion / overflow tank is pressure differential that occurs when the coolant gets hot, then cools. As it cools it would draw from the expansion tank and maintain 'equilibrium.' You have no vacuum in the coolant loop due to a bad heat exchanger. Perhaps a bad cap, but does not seem to be that based upon your test.


2. Losing coolant with no external leaks. Physics tells us the fluid has to go somewhere. You've already eliminated evaporation through the cap. Where else can the fluid go where it would not be seen? Ans: into the fresh water lines.


You may be able to prove this by taking the coolant cap off and leaving your water system pressurized. If you get water into the coolant loop then you know the bad news for certain. Or, if you can attach a pressure test rig to your fresh water inlet & outlet line at the unit that will tell you.


I don't pretend to be any kind of aquahot expert, but I've learned this through a few years experince working with heat exchangers of various types.


Best of luck - I hope it's not a $9K solution....
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Old 11-01-2021, 10:04 PM   #3
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Leak into the domestic water coil would only occur when the dometic water system is depressurized and boiler is hot. Domestic water system is 40-60 psi and boiler cap pressure is max 13 psi.

There is also an engine coolant loop - are you gaining engine antifreeze level? The coolant return line connects on low pressure side - return to engine overflow tank and water pump suction. It “could be” lower than pressurized/hot boiler tank.

Simple thoughts….

Brian.
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Old 11-02-2021, 02:21 AM   #4
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I would test each side. use a radiator pressure tester and bring the tank to 20lbs or so and turn off domestic and drain pressure to zero. see it the tank holds for a long time. I think i would also take of the in and out domestic line and put a test on that. In the old days i ran into situations where tanks would leak with thermal expansion so they leaked when warmed up but tested cold fine. The only other thing and this more more of a quess is can a leak in the heat exchange vaporize and go out as exhaust disguised as humidity?
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Old 11-02-2021, 12:37 PM   #5
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Hydro hot issues

Thank you all for your responses. Based upon the volume of antifreeze lost (3 qts in 3 days) I don't believe that the boiler antifreeze is getting into my hot water exchanger. I keep track of my engine coolant level religiously and it has not changed (although both fluids are red). The last thing that IASM said about the antifreeze leaking into the combustion chamber and being vaporized into the exhaust makes the most sense and is about the only explanation that makes sense.

Problem is, what do I do about it. Can the leak be found? Can the source of the leak be repaired? I have never seen the inside of one of these units, so cant imagine what might be leaking... is there a heat exchanger coil for the boiler antifreeze in the burn chamber? If so, can it be replaced?

Two different repair firms have drained the antifreeze, flushed the system and refilled, but never pressure tested. I thought that perhaps there was air in the system and that when it burped out the air, the antifreeze filled the gap. Seems unlikely given that I have added nearly two gallons the last two times the low coolant light kept the system from starting.

Is my only option having another repair firm(I am not physically able) drain the system and pressure test it? If so, can they visually inspect the line inside the burn chamber? Thanks again for sharing your knowledge.
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Old 11-02-2021, 02:15 PM   #6
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Was just wondering

If coolant is going into combustion would one not get white smoke like a bad head gasket in a vehicle?

Perhaps after first firing off and then diminish as unit gets hotter if it's a slow leak into the combustion chamber

Or perhaps a leak in the water pump itself and draining un noticed?
Just me wondering off again
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Old 11-02-2021, 08:57 PM   #7
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From the description and comments, the leak likely involves the hydronic heat circuit. A leak at the flame source will produce white exhaust smoke. There is a switch to disable the engine exchange. The usual operation is electric on and diesel enabled, but diesel only kicks in when the coolant temp drops, and then only runs for a minute or so.

Run the electric for a day or two or 4, but no hydronic heat and no engine circulation, then shut it off, wait till it cools, and check fluid in the tank. If the level is steady, on electric only run the hydronic heat for a day or two and check level. One of these two should show the drop in coolant level.
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Old 11-03-2021, 11:43 AM   #8
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Thanks everyone for the responses, they give me hope that I may not have to replace a $12K system on a 16 year old coach. In Colorado and Nebraska, we definitely need the diesel burner for heat. However, since we are headed to the Southern California desert where it rarely gets below 40, we should be able to get by with heat from the Coleman heat pumps on the roof. The electric element should provide enough hot water if we leave enough time between showers. Of course using this method, the hydronic fluid will never circulate or be under pressure, so it is unlikely that there will be any loss. At least we have this option to get by without the hydronic heat.

Running the furnace for a few days should tell us if we are still losing fluid or that perhaps we have finally chased all of the air out of the lines. If not and the loss of fluid persists, it may be time to take our lumps and trade.

Any other ideas are welcome!
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Old 11-03-2021, 04:26 PM   #9
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Where in SoCal. I will be in El Centro area starting mid November. Rio Bend. I could give you a hand.

BriAn
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Old 11-03-2021, 04:50 PM   #10
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Professional advice is available for FREE for the DIYer online at: Roger Berke: RV Hydronic Heater Repair: RV Hydronic Heater Repair - Home


Hydro Hot Service Quartzsite:
Lloyd De Gerald.
501 258 8426
Lloyd.degerald@gmail.com



Lloyd solved my leak problem
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Old 11-03-2021, 10:00 PM   #11
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Originally Posted by BrianGlenn View Post
Where in SoCal. I will be in El Centro area starting mid November. Rio Bend. I could give you a hand.

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Old 11-04-2021, 01:28 AM   #12
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has your unit ever been exposed to a freeze?
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Old 11-04-2021, 11:50 AM   #13
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regarding the Hydro Hot issues post

Has my unit ever been exposed to a freeze? Well, I don't know for sure because it had 12 years of history before I bought it. When we are not in Rancho California or on the road it is stored in a heated machine shed, so no not that I am aware of. The previous owners said that in the 9 years they owned it they never winterized it because they went to River Bend in Florida before the weather here turned cold.

Heat my RV serviced it for me in Aug 19 and all seemed to be well. In Jan of 20, the low coolant issue surfaced, I purchased a gallon of Camco refilled the tank and it gave no problems for the rest of the winter. Later in Feb 21, the low coolant issue surfaced again in CA. I contacted Howards RV, he looked at it and said the fluid was nearly molasses. I watched as he drained, flushed and refilled the boiler. During all of these sessions the unit never drew any fluid from the reservoir. Each repair service tried replacing the tubing, clamps and cap. Each said the tubing line was clear.

The unit worked normally until we got to the Oregon coast in Jun 21 when the low coolant issue started again. A few days later we arrived at Premier for other upgrades and I asked them to check the HH. They said the float switch was bad, coolant in tank low, and coolant tested at +12. They drained unit, flushed lines and radiators, replaced float switch and replaced fluid. We finished our business with Premier, traveled north to Washington and two days later the low coolant issue resurfaced and wouldn't fire up. Went back to Premier, camped in their lot overnight and of course the next morning after adding fluid, the unit worked just fine. Headed east into Idaho two days later, unit failed again. Added fluid to fill to the neck, coolant light would not go out. Took cold showers and tried to find an AH tech for the next few days until we got to Colorado.

In Colorado, Andrew with RV Repairmen came to repair, tested the system, said the control board was bad and also the float switch was inop. Took the unit all apart, showed me a stainless steel cylinder from the burn chamber that had a small crack and carbon deposits. (John Carillo had showed me the same piece two years earlier while servicing but said that it would affect the functionality.) Andrew replaced the cylinder, reassembled the unit and all seemed to be well. Unit was used only to occassionally make hot water during the summer and worked fine. The first time we needed heat a couple of weeks ago, low coolant light came on, refilled tank with a gallon of fluid, worked for 3 days, quit and took another 3 quarts to fill. Tested cap with paper towel on top, no steam escaping, no leaks on ground, no sign of lost fluid and expansion tank level has never changed. Go figure.

Is it possible that after 2 flushings and subequent refills, that there was enough air in the lines to absord more than a gallon of fluid each time?
Haven't used the unit since adding three quarts the other day, so I guess we will see...

Sorry about writing a book, but now you know the whole story. Thanks for your patience!
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Old 11-05-2021, 01:07 AM   #14
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Quote:
Originally Posted by daveb1256 View Post
Has my unit ever been exposed to a freeze? Well, I don't know for sure because it had 12 years of history before I bought it. When we are not in Rancho California or on the road it is stored in a heated machine shed, so no not that I am aware of. The previous owners said that in the 9 years they owned it they never winterized it because they went to River Bend in Florida before the weather here turned cold.

Heat my RV serviced it for me in Aug 19 and all seemed to be well. In Jan of 20, the low coolant issue surfaced, I purchased a gallon of Camco refilled the tank and it gave no problems for the rest of the winter. Later in Feb 21, the low coolant issue surfaced again in CA. I contacted Howards RV, he looked at it and said the fluid was nearly molasses. I watched as he drained, flushed and refilled the boiler. During all of these sessions the unit never drew any fluid from the reservoir. Each repair service tried replacing the tubing, clamps and cap. Each said the tubing line was clear.

The unit worked normally until we got to the Oregon coast in Jun 21 when the low coolant issue started again. A few days later we arrived at Premier for other upgrades and I asked them to check the HH. They said the float switch was bad, coolant in tank low, and coolant tested at +12. They drained unit, flushed lines and radiators, replaced float switch and replaced fluid. We finished our business with Premier, traveled north to Washington and two days later the low coolant issue resurfaced and wouldn't fire up. Went back to Premier, camped in their lot overnight and of course the next morning after adding fluid, the unit worked just fine. Headed east into Idaho two days later, unit failed again. Added fluid to fill to the neck, coolant light would not go out. Took cold showers and tried to find an AH tech for the next few days until we got to Colorado.

In Colorado, Andrew with RV Repairmen came to repair, tested the system, said the control board was bad and also the float switch was inop. Took the unit all apart, showed me a stainless steel cylinder from the burn chamber that had a small crack and carbon deposits. (John Carillo had showed me the same piece two years earlier while servicing but said that it would affect the functionality.) Andrew replaced the cylinder, reassembled the unit and all seemed to be well. Unit was used only to occassionally make hot water during the summer and worked fine. The first time we needed heat a couple of weeks ago, low coolant light came on, refilled tank with a gallon of fluid, worked for 3 days, quit and took another 3 quarts to fill. Tested cap with paper towel on top, no steam escaping, no leaks on ground, no sign of lost fluid and expansion tank level has never changed. Go figure.

Is it possible that after 2 flushings and subequent refills, that there was enough air in the lines to absord more than a gallon of fluid each time?
Haven't used the unit since adding three quarts the other day, so I guess we will see...

Sorry about writing a book, but now you know the whole story. Thanks for your patience!
Yes if air were in the system things behave different. You can get a radiator presure test kit from harbor freight and put it on a test at the cap pressure for a while and confirm it stays up. If it does fill the tank all the way to the top and see if it will cycle. It pulls coolant in on the cool down.
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