MemberJanuary 16, 2020 at 1:50 pm
You guys remember about 2 years or so ago, I put a thread up where we had to repair the bottom heat exchanger and the wall of the oven because it was cracked.
I went to replace igniters yesterday and guess what, top heat exchanger had a crack right in the center of the weld on the flange. The wall was cracked in 2 or 3 different places.
I don’t get it, how is that possible? It’s been like 4 years and in most cases this oven would’ve been totaled 2 times now since most people wouldn’t try to fix it.
Ended up getting some graphite gaskets made at a place in Tampa, FL where they made the gaskets fatter which will hopefully help seal it all up but my god, it’s just amazing how many fatal problems this unit has.
Any of you guys experience this on Rational or some other brand of combi?
MemberJanuary 16, 2020 at 6:51 pm
We have seven gas Rationals. Only had that happen in the floor model 202…which is ten years old now.
Is that Convotherm a spritz unit?
MemberJanuary 16, 2020 at 8:46 pm
It’s a GS so yeah a spritzer, no boiler.
It’s a 20.20 so it’s a floor standing model, what happened to your rational?
Drives me insane this thing.
MemberJanuary 17, 2020 at 2:59 pm
In your spritzer, I have to wonder if the blasting of cold water onto the blazing hot heat exchanger might cause stress fracturing. Also consider that any scale on the exchanger would insulate it and cause the metal to get too hot.
I’ve never cared for the entire concept of a spritz system for fear of their potentially unique problems.
My Rational uses a boiler. I was having issues with the bottom heat exchanger melting down the plastic vanes of the impeller in the burner blower. It kicked my butt. I finally conceded to my defeat after several thousand dollars in replacement parts. I was at my wit’s end, so my boss finally allowed an outside company (Whaley) to look at it.
He had FAR better eyesight than I did by pointing out a cracked heat exchanger. We let them do the repairs and it’s been good ever since. That was five or six years ago.
MemberJanuary 17, 2020 at 3:01 pm
Wow, well there you go. I guess it does happen.
Just seems odd that the manufacturer would design it to fail this way.
MemberJanuary 17, 2020 at 6:08 pm
WOW! That’s bad!
As is your situation, I’m pretty much running solo. Nobody else in my shop has schooled themselves up to work on Rationals…
(or Frymaster fryers)
(or Enviropak smokers)
Or pretty much ANYTHING that’s overly technical (or electronic-AL) always falls on ME.
So, when occasions arise when another set of eyes is in order, I have to continue mulling it over until I actually finally find the problem…or get someone in who’s factory trained.
SO far – in my eight years here, it was just that one Rational which required that. However, I might have another – but it’s on the back-burner for now as I have other ideas before conceding to IT.
MemberJanuary 17, 2020 at 6:17 pm
Good to know I’m not alone, lol.
I know the feeling, any technical piece of kitchen equipment ends up on my bench.
MemberJanuary 17, 2020 at 6:43 pm
I finally conceded to my defeat after several thousand dollars in replacement parts.
So, the big question is what did you learn from it?
MemberJanuary 18, 2020 at 11:45 am
That I need to get my eyes checked! LOL!
No, I’d never even considered the possibility of a crack in the exchanger, much LESS it causing flame to backdraft into the (…ahem…) PLASTIC burner blower wheel.
Maybe they cover that at the Rational training seminar in Chicago. I don’t know because I haven’t been to it.
MemberJanuary 18, 2020 at 11:51 am
It’s amazing what can escape through a crack. I mean when the bottom burner cracked, the blower cover was partially melted and so was the ignition board, the crack wasn’t even big but I guess the heat was so intense it just managed to lick it enough.
MemberJanuary 18, 2020 at 4:11 pm
combi ovens that use a spritzer to make steam , no matter who the manufacturer, will look like crap inside from the scaling and are far more likely to crack a heat exchanger from the thermal shock . an observation over the years…
MemberJanuary 17, 2020 at 6:32 pm
Interesting stainless burner chamber. What caused the the hot spot. Flame impingement? Burner distortion? Fuel air mixture?
That takes serious heat to do that.
Now where precisely are they adding the water to it?
MemberJanuary 17, 2020 at 9:44 pm
Good question, I honestly don’t know.
It could’ve been delayed ignition perhaps? That’s the only thing I’ve noticed.
This heat exchanger can also glow red hot, according to Convotherm that’s perfectly normal but that I’m sure isn’t helping.
The water gets sprayed into the center of the blower wheel which is in the center of the heat exchanger and it wraps around it, so it’s hard to say exactly where as it just gets flung all over the place.
MemberJanuary 18, 2020 at 9:57 am
Delayed ignition will not do that with Gas. Neither will the water on the outside of the heat ex-changer. But a burner that has a irregular flame will. Like a obstruction pushing the flame to on side or a flame arrestor partially plugged or with a hole. And if it is a burner with secondary air injection, look for a blockage of the air flow. Allowing the main flame to hit that area. Your a welder, so you know how much heat it takes to oxidize that special high temp material like that.
MemberJanuary 18, 2020 at 11:50 am
Interesting, unfortunately this burner has no glass in the flange where I can look into the chamber when it’s lit like it’s little brother does (OGS model) I’ll have to see if I can figure it out.
Red glowing stainless is probably not stainless anymore, most likely the chrome was burnt off which is why it’s so black and that does take a serious amount of heat, no doubt a burner could do it, but I would think the heat transfer would have been designed in such a way to prevent it.
Guess not, makes sense why it’s having this many fatal problems, piss poor design.
MemberJanuary 18, 2020 at 4:27 pm
It’s still a stainless, but I don’t know whether it’s in the 300 or 400 family. and you can bet a very special alloy.
MemberJanuary 18, 2020 at 7:27 pm
It could be a special grade of stainless, but regardless, to be classified as stainless it has to contain over 15% or so chromium, and chromium is one of the first elements to go if overcooked, which is why “sugared” or “candy flossed” welds are so dark, it’s the chrome missing which removes it’s shiny surface.
Then it becomes prone to rusting.
Welds like 308 or 304 though, nothing special there.
MemberJanuary 18, 2020 at 7:47 pm
Now ya’ll are talkin’ WAY over MY head.
I’m just a BLAST welder. Oxy-acetelene. MIG or TIG.
Whichever! It ain’t purty when I git done!
MemberJanuary 19, 2020 at 8:41 am
We all gotta start somewhere 😀
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