Aqua Hot Burner Controller Improvement

[Edward Buker]

The Aqua Hot uses a Webasto burner that has been around for quite some time. It has a controller in a metal case that slides onto the side of the burner. In the Aqua Hot design all of this resides within an insulated enclosure. This is a very hot environment for electrical components and it is especially so for this old design controller given that it employs mechanical relays with springs. As this unit ages in this environment they are prone to fail and the cost is between $500 and $800 for a new controller. I have had to replace this once in my coach and I did not want to face this again.

There is enough wiring harness to move the controller to the outside of the cabinet which is what this post deals with. This modifcation takes about two hours and it involves drilling two holes for the mounting clip and two slotted holes to accommodate the exit of the wiring harness. I used a drill press and a step drill to drill the two small mounting holes and the step drill to a diameter of 3/4 inch for the slotted holes used for the wire exit. I used a dremel tool with a metal cutting disk (I like EZ LOC type) to extend the holes to the edge of the cover. The mounting is on the back right of the front cover. The unit barely gets warm now and should last the life of the Aqua Hot. When removing the cover you simply unclip the controller and drop it inside the Aqua Hot base to the right of the burner while servicing. I protected the wiring with some Velcro at the exit point, grommets, tape, etc will work here.

Later Ed

[Bill Sprague]

Interesting!  I had one fail too.  It was apparently mounted upside down in the clip by Beaver.  One of the PEX fittings on the back was not tight and was leaking which turned the whole cabinet into a steam bath.  With the upside down controller, water collected on the "bottom" and penetrated the housing.  Inside are three or four very small mechanical relays.  One didn't like being wet.  

Had it been installed like you've done, I may not have had to spend the $900!

[Orman Claxton]

There is a rebuilt controller available,
BUT, I will not sell one or use one.
I can't trust it to last.

[Edward Buker]

Bill,

Wet relays just are not happy....

Orman,

It is your reputation at stake and if you are not sure that the rebuilt one will last then you have to follow your instincts. One of the common fail modes is when the blower cool down cycle will not shut down properly. That one is caused by a relay spring that has lost the right temper and becomes weak due to heat fatigue. It tries to release and the blower speed waivers but it continues to run.

You cannot buy these relays best I can tell from searches I have done. I was going to rebuild my own as a back up but the parts just were not available. Orman, you may want to consider offering this modification, if anyone would like it done that is not comfortable doing it. If you did one and had a marking template it would be relatively easy compared to a lot of jobs that you have done already on these units. The bracket mounting location has to be low enough to clear the expansion tank when removing the stainless cover. Drilling stainless is easier with a drill press so that may be an issue. I cannot speak to all the wiring harnesses but my controller had just enough wire length to make this work.

 I think in most of the non Aqua Hot applications these Webasto burners were more exposed to ambient air. In this case you have the controller on the side of a hot burner and then you enclose that in an insulated enclosure that sits at 190 degrees. Not many electronic items would last very long in that environment....

Later Ed

[Bruce Sieloff]

Apparently this is going to be an increasingly sensitive fail point as our rigs age.
 
Maintaining complicated systems with aging or non-existent parts requires some reengineering challenges
.
I am familiar with a couple of rebuild techniques to maintain the heat exchanger (search the forum for Aqua Hot Hacks) to avoid an $8K replacement.
 
This seems like a good opportunity for someone to design a solid state controller for this unit.
 
Certainly we should be able to do better than $900 for old parts, and have a unit with increased reliability and maybe improved functionality.
 
Given the current state of electronic fixes available, from programmable logic chips, raspberry pi computers and solid state relays, I would think that a sufficient number of presales for a redesigned unit might encourage and inspire folks with the expertise to design and align themselves with a builder and knock out a few copies of an Aqua Hot controller.

There are a lot of Aqua Hot units installed out there, the customer base should be substantial enough to make it worthwhile.

I would sign up for one.  

[Edward Buker]

Bruce,

I have thought that this would come to pass at some time but so far nobody has taken the plunge and designed and built a replacement. I think the volume is low enough that it just will not make a good enough business case at lower prices.

Later Ed