What is now causing this? Thanks
Sound like a control problem. I'll defer to ectofix on this, But he'll need a model to be accurate.
Frank asked: What's the cause?
W-E-L-L...the high-limit is either doing its job, or it's faulty.
Such a short question for wanting to resolve a problem with so many possibilities.
The high-limit's job is to sense excessive temperature in the steam generator when there's a lack of water. In a Rational combi-oven, it opens at 260-ish°F (125-ish°C). Its there to protect the element(s) from damage due to dry-firing, or worse - the meltdown of hoses, tank insulation, wire insulation...or a fire.
Here are some of my questions:
I could keep going.
Like fixbear said, there might be a control issue. The element(s) shouldn't be energized until the water level probe senses the presence of water. If that water probe is bridged to ground somehow...or the water control circuit within the board has failed, then the control board might be seeing water when it's not really there. Thus - not calling for the generator to fill and thereby proceeds into its next step...energizing the elements.
Another possibility is the heating element's control relay, contactor or SSR(s) is stuck closed - thereby keeping the element(s) energized despite the inadequate water level. This would less likely be your problem since, assuming the water level control portion of the board is good, it would've had the steam generator full of water once you'd reset it and it tried heating again.
For the control circuit, these are thethings immediately come to mind. However, a seasoned tech will see other possibilities. I would too. However, I'm not going to wear myself out here proposing any and every other possibility here.
Aside from the control circuit, THEN there's the possibility that the actual high-limit is faulty. If the generator proves to always have the proper water level in it, then it's impossible for the temperature in the generator to exceed 212°F (100°C). If this is confirmed to ALWAYS be the case, then the high-limit is faulty.
FINAL NOTE: Anytime I'm ever been called upon to work on a steamer or a combi-oven that might be having water control or water heating issues, I ALWAYS pull the water level sensing probe(s) from the steam generator for an inspection.
99% of the time I'll find scale ON the probes or in contact with scale somehow. SCALE can cause NUMEROUS problems within the generator. With regards to the water probe(s), I've seen scale completely insulate a probe's ability to sense water (no heat, constant over-filling)...or do exactly the opposite...by providing a bridge of moisture that's JUST adequate enough to bridge a water probe to ground (no water fill, dry-firing of heating elements)
ANYWAY - the above is the simplest response that I can offer to your question.
Based upon your question, I can quickly presume that you're not a technician. I DO suggest that you get one to look at it.
With questions like these I feel like giving them the simplest answer.
Its broken. That's your problem.
But then I restrain myself.
Ectofix seems to have nailed it pretty good, I had a toaster oven last week where the high limit was bad, kept turning the unit off so it does happen.
Steamers are not a force to be reckoned with unless you know what you'r doing especially on high limits and safety features.
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