I would throw this issue back to the manufacturer. An oven that cannot cook at the temperature it's set at is worthless. Maybe you have a 'lemon'.

It is way past warranty so i am looking for clues to what might be going on.

You have actually tested the temp inside the oven with a hand held thermometer assume. So when was the last service call on this isssue? IMO since these are made in the US there should be some way to talk to an actual person to see what can be done warranty or not .

Thank you to those who have responded. I am new to this forum so I guess I might have been a little naive to expect people to read my OP and see that I have had this range for many years, and that I did work with capital under warranty during the one year warranty period. One fact I didn’t include in the OP was that the third warranty repair in the first year was slightly past the year and Capital graciously extended coverage.

It probably is a good idea to contact Capital again to see if they have advice on what the issue might be, so I will try that also.

But i was hoping to get clues to what might be the issue here.

@rwiegand

It was your post that made me consider the igniter. I have saved a link so I can try swapping the part. Did you have a parts diagram to work from? As a DIYer I don’t have experience working on ranges, let alone this model.

Since setting the dial to 350 results in an internal temperature of 350 degrees I was considering the thermostat less likely to be the issue.

My train of thought was that a weak igniter part might be tripping on and off on a short cycle after getting over a greater than 350 degree temperature.

To be perfectly honest I hoped that someone on this forum would have experienced this issue and would have a ready answer.

The usual failure mode for igniters is to gradually slow the gas flow. You start noticing that the oven takes an extraordinatily long time to pre-heat. It may not be able to maintain a higher temperature. No idea what, other than the thermostat, would cause it to go over temp.

The ignitors come in several sizes, here's a link to one; you should match the length to the one you have. The numbers are 41-20X for the different sizes. A couple different lengths actually work in the CC. https://www.furnacepartsource.com/robertshaw-41-203-ignitor/

Sorry, no manual or parts diagram, I just take stuff apart to see how it works. (Unlike when I was a kid I actually manage to get most things back together again now.)

Is Capitol still in business? I'd had the impression that they had folded.

Thanks,

There still seems to be some confusion created by my OP. My apologies.

The overheating issue was due to lack of air flow around a full size commercial baking sheet. That is my diagnosis, as the tech replaced the thermostat three times without resolving the issue. Using single half sheet pans per rack does not trigger the runaway heating issue, so i am pretty convinced.

The current issue, four or five years later, is about the oven not getting up to temperature when set above 350 degrees. Hence my thinking it might be the igniter safety circuit.

Capital does appear to still be in business as their website, capital capital-cooking.com, is active and has a 2021 copyright notice. But I will know for sure after I call tomorrow.

Thanks

Thank you for your replies. I just got off the phone with Capital service. Superior Equipment Solutions now owns the brand.

The oven has now started having the overheating issue again. A few days ago I was making chicken wings and set the oven to 425. It continued heating to over 550 based on two oven thermometers I keep in the oven.

The service guy at SES suggested that the thermostat was bad. I reminded him that I had three thermostat replacements under warranty and none of them fixed the problem. I then suggested that perhaps a valve was getting stuck open when at higher temperatures. He thought about it, agreed that it was unlikely that all four thermostats were bad and suggested the igniter, which was discussed earlier in this thread.

He also stated that he has not had this issue reported to him, so we were just discussing theories. That is a good news/bad news for me. The good news is that this doesn’t appear to be a design issue. The bad news is he doesn’t have an answer. He told me the igniters are more prone to going out before the thermostat and he hasn’t heard of a valve having issues.

The support tech also suggested measuring the circuit at different points to determine what the the components are doing.

I asked if there was a parts manual/diagram and the tech said that none existed at Capital when it was acquired. All he has is a partial list of parts.

So my next step will be to acquire a igniter and see if that fixes the issue.

Since reading this I acquired an appropriate remote air temperature probe for my electronic thermomenter and have been monitoring the temperature in my oven-- it's all over the place. Consistently nearly 50 degrees higher than the dial on the front would indicate, but also with 100 degree spikes while cooking-- when set at 350 it will generally record a high actual reading of ~475. I don't have a data logger for the thermometer, which would be very useful to see what the pattern looks like-- ie whether those spikes are prolonged enough to be problematic. The thermometer only notes the highest point.

There's also a lot more unevenness than I would hope for in a convection oven. the back left corner is particularly hot. I've known for a long time that I need to rotate trays of cookies, for example.

I installed a new ingiter a couple months ago.

This shouldn’t be that hard to figure out. My understanding is that the components are thermostat, igniter, solenoid, valve and burner. And the technology is mature and it’s characteristics well known. Unlike the ovens that incorporate electronics.

Just reinforcing that the igniters can be bought via Robert Shaw part numbers - Robert Shaw does not make the part it is actually coorstek (formerly Norton) 501A is the base part then it gets different ceramic insulators and covers. the Robert Shaw catalogue is here and you can cross reference by part length. https://www.robertshaw.com/WorkArea/DownloadAsset.aspx?id=2147496739 Robert Shaw part for a 49 culinarian small oven is 41-204 my assumption is the large oven should be the same and prob the broiler as well. But if you measure you can then get the correct part for about $30. You will have to crimp your own fast on connectors on unless you want to switch to wire nuts (im doing connectors)