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Old 10-25-2021, 01:09 AM   #1
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AquaHot 450D Startup Problem

I have been experiencing an unusual problem with the AquaHot installed by my 2007 Allure's previous owner in 2012 as a replacement for the original HydroHot. Since I purchased this Allure in 2017, I have regularly serviced the AquaHot 450D, replacing the orifice, fuel filter & cleaning the entire burner assembly but have had a Diesel burner startup problem.

Whenever I take my RV out of storage, bring the RV home & turn on the Diesel burner, the Webasto burner does not fire up. I found that by plugging in to shore power, turning on the electrical element & waiting until the Aquahot boiler is up to temp, turning on the diesel burner results in consistent operation of the Webasto burner. Once the Diesel burner fires up, the Aquahot unit operates consistently, without failure for several days to several weeks at a time.
Any ideas on what would cause this problem. It almost seems like the diesel fuel runs back to the fuel tank because when the diesel burner finally does fire, it smokes for 10 - 15 seconds as though there was air in the fuel line.


Felix & Becky
2007 CC Allure Sunset Bay #31448
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Old 10-26-2021, 10:51 AM   #2
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Do you align the igniter tips each time? Sounds like a cold startup issue and possibly a low 12V (house batteries after storage?) - weak igniter spark?

As we know diesel loves to ignite in a warm environment, vs cold one.

My 2007 Allure (31563) came with the 450DE1 AquaHot from factory. It is listed and serial number on the factory Serial Number ID sheet on the back of the vanity door.

My thoughts.

Brian
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Old 10-28-2021, 12:40 AM   #3
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Thanks for your input, Brian. The igniter can be heard 'snapping' with each repeated attempt to fire the diesel. The gaps on the igniter rods have been adjusted numerous times with no improvement. I currently have 900 AH of brand new LiFePo4 batteries that replaced four AGM 8D batteries & have experienced this Aquahot problem with both sets of batteries since owning my Allure.


I am very tempted to remove the fuel line from the filter inlet and temporarily plumb in an external tank of diesel fuel. Or, would adding a fuel pressure gauge AFTER the Webasto fuel pump reveal a defective fuel pump?


What really has me stumped is that after warming up the Aquahot for an hour or so, via the electric element, the diesel burner fires up (with some white smoke on the very first ignition) every, single time, consistently & with NO smoke. A that point, I just turn off the electric element and can use the diesel burner mode for weeks on end, from 100 degree down to 5 degree weather.


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Old 11-10-2021, 06:53 PM   #4
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How cold is the weather?
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Old 11-10-2021, 07:03 PM   #5
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Quote:
Originally Posted by fstruys View Post
It almost seems like the diesel fuel runs back to the fuel tank because when the diesel burner finally does fire, it smokes for 10 - 15 seconds as though there was air in the fuel line.


Felix & Becky
2007 CC Allure Sunset Bay #31448
That's possible, but doesn't explain why the burner would act differently when the boiler fluid has been heated by the electric element
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Old 11-10-2021, 07:43 PM   #6
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It always fails to start on Diesel in cold weather; it starts after multiple attempts in warmer weather. If I get the AquaHot warmed up to temp in Electric mode, with the RV plugged in, then once I select the Diesel mode, it will begin to work & continue to do so perfectly without any failures in any weather for as many days/weeks while we're RVing. Whenever I have shore power, I'll plug in my RV and use both the Electric & Diesel modes.

After the AquaHot is up to temp & I select Diesel mode, I get a fair amount of white smoke on the first firing of the Webasto burner. After this first "smoke" event, it never smokes again. This leads me to suspect that air is getting in the fuel line between the fuel tank and the AquaHot, with, perhaps, a small leak in the fuel line that allows the diesel fuel to drain back into the fuel tank, but I don't find spilled fuel anywhere.

I have read multiple posts about issues with Aquahots having problems when cold but working correctly once it's warm. Perhaps a 'cold' fuel pump or ignition coil are causing my Diesel-mode starting problems? I have been annually changing the fuel filter & nozzle as well as thoroughly cleaning all the burner parts & checking/adjusting the electrode spark gap.


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2007 Allure Sunset Bay #31448
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Old 11-12-2021, 09:11 AM   #7
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I had been thinking I had a leak in the Diesel pick-up tube for my Aqua-Hot. So I drove the coach a few miles to get it fueled up. It took 35 gallons to top it off. When I got home, the Aqua-Hot fired right up although it had some white smoke for a while. That was most likely due to retained fuel form previous failed starts.


Now, after reading some posts about reluctance to start up when cold, I'm going to try a heat gun in the intake next time. I am so tired of pulling the burner to verify that everything is OK (which it always is).


If that works, I'm going to get a cheap spare heat gun and put it in the cargo bay so that I can have one handy.


I wish there was an affordable propane conversion for this finicky beast.
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Old 11-13-2021, 12:01 PM   #8
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I guess I am at that point where you start replacing parts to solve the problem. A number of posts I've read imply that by having the AquaHot up to temp with the Electric mode, then switching to Diesel mode to successfully continue using the AquaHot, does NOT necessarily suggest a Diesel mode start-up failure as caused by a diesel fuel supply issue. Having the AquaHot up to temp, I have read, increases the likelyhood of correct fuel ignition as everything is warm.

So, if I had a poor diesel fuel ignition problem, it would less likely fail when things are warm. Perhaps that's why once the AquaHot is up to temp & I switch to Diesel mode, having everything warm simply insures an adequate diesel ignition cycle, preventing the re-occurrence of any further Diesel mode problems.
But which part gets replaced first? From reading several forums regarding AquaHot problems, I'm going to order/replace the ignition coil. I'll post my progress.


Felix & Becky
2007 CC Allure Sunset Bay # 31448
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Old 11-13-2021, 12:37 PM   #9
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Does the level in the expansion tank rise and fall normally when the boiler is heated / cooled?

Is it possible the unit is low on boiler fluid, preventing the burner to fire, untill the electric element heats the fluid, raises it's level enough to satisfy the level sensor?
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Old 11-13-2021, 01:04 PM   #10
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Ours smokes when it has been in storage to long without running. When winterized, with the pink stuff I run it at least once a month.



Professional advice is available for FREE for the DIYer online at: Roger Berke: RV Hydronic Heater Repair: RV Hydronic Heater Repair - Home

Roger has advice and pictures for free, and sells parts.
Hydro Hot is the older versions of Aqua Hot
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Old 11-14-2021, 02:08 PM   #11
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Yes, the coolant level does rise & fall during use. Funny thing, when I bought this RV, I found the expansion tank mounted with its bottom below the top of the AquaHot cabinet. I noticed that there were many air pockets/bubbles in the hose connected to the bottom of the tank.

I decided to relocate the tank so it's now well above, maybe a foot higher, than the AquaHot cabinet, then replaced the vinyl hoses with clear, high-temp silicone hoses. I have kept a very close eye on maintaining the fluid within the high & low levels marked on the expansion tank. I'm not sure how many AquaHot users know that the correct procedure to add coolant is through the drain hose in the bottom of the AquaHot cabinet, thereby preventing air pocket or bubbles.


I will replace the ignition coil next, but am not very optimistic this is the fix.


Felix & Becky
2007 CC Allure Sunset Bay #31448
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