Combi Oven Uneven Cooking

[olivero]

Interesting, fair enough.

 

I figured the delay is not really intentional but more of a verification process, ensuring the top is lit before lighting the bottom. in most cases, they light within a minute of eachother. As soon as the *boom* is heard of the top one, the combustion blower starts running on the bottom one and the lighting sequence begins.

 

The ignition modules are the same, the igniters are hot surface ignition.

[fixbear]

With hot surface, age of igniter and voltage/resistance cause huge variations.  IF they are staging the ignition, it should be bottom then top..  But when I looked at the wiring, they were fed together. Therefore should lite very close together if correct.  I’ve never been a fan of hot surface. I’ve seen several of the same igniters within the same brand take a big difference in ignition time. It’s just plain hard to control Silicone carbide.

[ryantruck9]

I believe Bush is on the right track.

Had a similar experience with floor model

there was a time when Cleveland’s HSI’s were crap (maybe still are?)

due to constant problems on a unit under warranty I was instructed to increase the trials for ignition from 2 to 4 trials

months later the customer had the exact same complain you have written.

they also had pictures of the entire roll cart of food and you could see the difference.

I could watch the unit after preheat light top burner fine but would take 3 or all 4 trials to get the bottom burner lit

 

the trials for ignition are quite long with prepurge and HSI heat time so effectively the bottom was running well below temp.

if as Bush says the top burner managed to satisfy the call for heat the food didn’t stand a chance

the bottom could be 100-150F lower than the top and its no longer calling for heat

 

is your unit set for 2 trials for ignition? that could be around  7 min to lock out

if 3 or 4 trials we could be talking 13-15 min before an error is recorded assuming it didn’t already satisfy the call for heat.

 

Let us know when your facility eventually replaces that machine, perhaps we all book some time off and take it to an empty field with a cooler and some guns

(I’m Canadian so you guys bring the guns, i’ll bring the cooler)

[olivero]

Okay, I’m sold. I’ll give it a shot and see, sounds like it could be it. Cleveland told me to raise the ignition attempts to 4 a long time ago as there was frequent ignition problems (just bad igniters).

 

Im gonna go see if its on, might be able to get some ohm readings by the time you read this.

 

In regards to the empty field idea, Sounds like a great plan, much better than the spot in the dumpster I had reserved for it.

 

I’m Danish, so I’ll bring the oven.

[ectofix]

I hope that’s the problem…so we know you found the problem.

 

While ya’ll were talking, I took a quick view of the service manual.  I would expect the oven would show some derivative of  E05.XX error code if the bottom burner wasn’t working.  However, being set for more trials before lockout, maybe INDEED the time before locking out got extended long enough to presumably cook a batch of food.

 

By the way, I have the space to perch that oven up for some target practice.  Only one one gun, though.

[olivero]

Right, that’s kind of what I was figuring, I think if you were to preheat the oven, for sure the bottom burner would have to fire, no way the top could do it alone before the bottom would error out. But making up for 10-20* I could see that, cook pork or meat 20* below what it needs and I believe pink meat is what you get in which case it would make sense

 

Next chance I get, I’ll check. Does if the burner is hot or cold make a difference? I seem to remember seeing odd readings when its hot and normal ones when its cold (room temperature)

 

Lol, sounds good.

 

Edit

 

I checked both just now, Bottom is 6.3 ohms, top is 4.2 ohms. Timed the ignition, they are 14 seconds apart and it lights on the first attempt.

[ryantruck9]

It can make a difference for hot and cold burners on ignition. 

And with a heavy load the oven was probably working hard to recover after initial loading.

Perhaps a micro amp test during a heavy cook cycle if possible? 

Superheated flame rod starts to drift off burner?

Ignition module messing around?

Test hot micro amps and swap top and bottom modules?

If its an intermittent module the chefs might think they didn’t set the right time it all underdone

[olivero]

Haha, I could defnetley do all those.

 

I spoke to one of the chefs this morning, she said its not just the OGS unit, its also the Convotherm 4.

 

I had understood the OGS was doing it much worse but she said they are both as bad. 

 

Might just be the way those ovens are.

[fixbear]

Are they baking open or covered?  The reason I ask is steam bleeding into combustion mix will effect ignition. and flame quality.  Is it possible that oven leakage is getting to the burner intake?  Again, you have mentioned door leakage,  but how about kitchen air turn over?  Combined all together they may become cumulative and effect the available O2 .

[olivero]

Open.

 

The air intakes for the venturis come from the control panel, the steam tends to get pulled up and to the side as they are under hoods. The only time steam makes it under the oven is if there is no rack in the unit. It definetley doesn’t make it to the second combi. The make up air is also present, definetley not a problem.

 

Good thought though.