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Originally Posted by ECtofix

Words of CAUTION:

That Fenwal tstat has no built-in stops. SOOO...when you get the new one in hand, it's best not to do ANY unfettered turning of its stem - or else you'll ruin it. Just get it mounted and then follow the book on setting it up for calibration. You'll be installing its stops when you put all its connecting stem parts together inside the fryer.

Wasn't sure if that was in the manual, so just offering my requisite warning that I was told years ago and passing on to you.

Got it. I read excessive turning damages it

Originally Posted by jman2794

I can see I will be calibrating even the new though.
Look like I will measure oil and set the dial to the oil temp than tighten down Allen screws on the Fenwal sensor stem when the actual temp and dial align.
Does that sound right??

Words of CAUTION:

That Fenwal tstat has no built-in stops. SOOO...when you get the new one in hand, it's best not to do ANY unfettered turning of its stem - or else you'll ruin it. Just get it mounted and then follow the book on setting it up for calibration. You'll be installing its stops when you put all its connecting stem parts together inside the fryer.

Wasn't sure if that was in the manual, so just offering my requisite warning that I was told years ago and passing on to you.

10/4 will do this

See ECtofix's link to the service manual. Page 1-8.

I can see I will be calibrating even the new though.
Look like I will measure oil and set the dial to the oil temp than tighten down Allen screws on the Fenwal sensor stem when the actual temp and dial align.
Does that sound right??

Originally Posted by LakesCo

From your description, this thermostat is stuck closed.

For example, at a set point of 200, does the fryer continue to heat until the high limit opens?

With the fryer warmed up (less than high limit cut off) and oil temperature verified with a probe, turn off gas supply, disconnect thermostat wires from gas valve and verify with a ohm meter that the thermostat contacts open and close in relation to set point and actual oil temperature. This will show if thermostat is cycling.

Let us know what you find please.

The stat setpoint was 330 and the oil temp was at 410 degrees and the main valve was still engaged until I lowered the stat to the lowest setting did the burner shut off. I did see the adjustment capability between the dial and Fenwal stat (thanks to last pictures I know what to call the sensor) but due to such a large differential it's not something I thought was close enough for calibration.

It sounds like you are describing the stat on the bottom of the pick. The Fenwal stat. This is Frymaster's Cadillac thermostat for millivolt fryers. I don't often see them fail, but it sounds like yours could have gone belly up. If it were me I'd test it like Lakesco suggested. If it's not stuck closed you could try to calibrate it but if it's more than 50 degrees off, it's time for replacement.


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From your description, this thermostat is stuck closed.

For example, at a set point of 200, does the fryer continue to heat until the high limit opens?

With the fryer warmed up (less than high limit cut off) and oil temperature verified with a probe, turn off gas supply, disconnect thermostat wires from gas valve and verify with a ohm meter that the thermostat contacts open and close in relation to set point and actual oil temperature. This will show if thermostat is cycling.

Let us know what you find please.

Originally Posted by jman2794

well EVEN when someone does school me on the system its not used often so I forget. \
I have definitely been schooled here. Thanks to everyone

here is what i found
thermostat dial is connected to a two wire sensing element in the well of the fryer tank. The actual dial is just that only a dial: the well holds what looks to bea two wire sensor that has a rotating indicator that is hooked to the temperature dial on the front of the fryer through a flexible shaft. The entire system is a simple milivolt system ( i know thanks the info in this post). The setting on dial is 320 and the oil temp is 400 and still burning gas until it trips i lower the thermostat to the lowest setting does it turn off but by than the differential betwenn set point and actual is well over 100 degrees. or at times the gas valve will open if I tap the sensor for temperature control> I read the manual and as it and several people have said the limit (auto reset) will open at about 415 degrees.

Originally Posted by ECtofix

If there's an issue with the pilot burner, that's certainly a possibility. Crud buildup inside it - around the pilot orifice - can cause a poor, weak flame.

Then again, there could be several other possibilities. For instance:

• If the fryer is connected to gas by a flexible gas hose with quick-disconnect...and if the quick-disconnect isn't fully seated but allowing SOME gas through, it may starve the pilot when the main burner comes on. That could cause a slow drop in thermopile output - enough so to cause the combination valve to lock out.
• Could be it has a line gas pressure regulator (in addition to the combination valve's internal regulator) that's not regulating (due to maybe a clogged air vent), thereby affecting overall gas pressure. Once again, that will starve the pilot to a point that thermopile output drops.

To figure this one out jman2794, you should be there to watch it as the pilot drops out.

• Stay abreast of the actual oil temperature near the thermostat and high-limit.
• Monitor the thermopile circuit with your DC voltmeter.
• Check for any voltage drops in that circuit - like ones caused by a faulty, cruddy connection or a failing high-limit. Voltage drops in a millivolt circuit can be significant, since a fraction-of-a-volt isn't strong enough to punch its way through funk in a wire terminal or high-limit contacts that are weak.
• Monitor DC voltage across the terminals supplying the pilot solenoid. Monitor voltage from the thermopile to see if it's slowly dropping when the main burner is on.

I could go on. These (and the things mentioned by others here) are just some rudimentary tests to do on ANY millivolt fryer. I know you HVAC guys don't get to play with these basic systems very often. The closest you might come to them is an occasional gas water heater.

Millivolt systems are so straight-forward and simple that they can be intimidating.





Here's a video of a bench test I did on one of those fryer's burner system...just for the fun of it:

well EVEN when someone does school me on the system its not used often so I forget. \
I have definitely been schooled here. Thanks to everyone

here is what i found
thermostat dial is connected to a two wire sensing element in the well of the fryer tank. The actual dial is just that only a dial: the well holds what looks to bea two wire sensor that has a rotating indicator that is hooked to the temperature dial on the front of the fryer through a flexible shaft. The entire system is a simple milivolt system ( i know thanks the info in this post). The setting on dial is 320 and the oil temp is 400 and still burning gas until it trips i lower the thermostat to the lowest setting does it turn off but by than the differential betwenn set point and actual is well over 100 degrees. or at times the gas valve will open if I tap the sensor for temperature control> I read the manual and as it and several people have said the limit (auto reset) will open at about 415 degrees.

Originally Posted by buford

My thinking was maybe the main valve being closed by the t-stat was sucking the pilot flame off the pilot.

If there's an issue with the pilot burner, that's certainly a possibility. Crud buildup inside it - around the pilot orifice - can cause a poor, weak flame.

Then again, there could be several other possibilities. For instance:

• If the fryer is connected to gas by a flexible gas hose with quick-disconnect...and if the quick-disconnect isn't fully seated but allowing SOME gas through, it may starve the pilot when the main burner comes on. That could cause a slow drop in thermopile output - enough so to cause the combination valve to lock out.
• Could be it has a line gas pressure regulator (in addition to the combination valve's internal regulator) that's not regulating (due to maybe a clogged air vent), thereby affecting overall gas pressure. Once again, that will starve the pilot to a point that thermopile output drops.

To figure this one out jman2794, you should be there to watch it as the pilot drops out.

• Stay abreast of the actual oil temperature near the thermostat and high-limit.
• Monitor the thermopile circuit with your DC voltmeter.
• Check for any voltage drops in that circuit - like ones caused by a faulty, cruddy connection or a failing high-limit. Voltage drops in a millivolt circuit can be significant, since a fraction-of-a-volt isn't strong enough to punch its way through funk in a wire terminal or high-limit contacts that are weak.
• Monitor DC voltage across the terminals supplying the pilot solenoid. Monitor voltage from the thermopile to see if it's slowly dropping when the main burner is on.

I could go on. These (and the things mentioned by others here) are just some rudimentary tests to do on ANY millivolt fryer. I know you HVAC guys don't get to play with these basic systems very often. The closest you might come to them is an occasional gas water heater.

Millivolt systems are so straight-forward and simple that they can be intimidating.





Here's a video of a bench test I did on one of those fryer's burner system...just for the fun of it:

I will be checking the thermostat against the oil temperature. Since the limit may be doing its job

First off I want to thank every one for the help. The manuals, the pictures, and the tech tips. This place ia full of unselfishness; never fails.

The cooks say after I left the oil warmed up and they cooked some than it shut off they've had to relight the appliance pilot several times in the time since thermopile replacement Last Friday ( 2 days ago)..
Prior to repair it would always shut off or extinguish the pilot after the oil would get hot. In other words cold start no problem, once the oil got hot the pilot would shut down and not stay lit when reattempting to start according to cooks. My first intuition was replace the thermopile it was also the most recognizable part to me. As i was installing the thermopile I saw the limit wirng could break the pilot circuit the manuals and your input confirm this. Sounds like Hi limit
Now I have things to look at when I get there today and will update.

Originally Posted by buford

My thinking was maybe the main valve being closed by the t-stat was sucking the pilot flame off the pilot.

i can check that too

My thinking was maybe the main valve being closed by the t-stat was sucking the pilot flame off the pilot.

Originally Posted by buford

The main gas goes off the same time the pilot does?

Of course. The pilot safety valve comes before the main valve in the gas train.

Here's the standard components inside a combination valve. The one flaw in this illustration is that PILOT gas is ALSO cut off by the safety shut-off valve. As VanMan812 had stated, pilot gas supply does come before the internal regulator:

The main gas goes off the same time the pilot does?

I just got my Frymaster book back from my last trainey and it so happens to be handy. Here's some info on how to test their millivolt fryers.





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Originally Posted by r22coolguy

Yes, but every hi-limit that I have seen on a fryer is Mechanical and needs to be reset. Since he didn't know there was one, nor has he reset anything I can assume that it's not tripping the hi-limit.


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As far as intermittent pilot outages on millivolt fryers (I don't think jman's problem is intermittent) my very first step is to test the hi-limit. They are a snap disc type of contact, as ECtofix already said, and any bit of jostling can make the contacts momentarily separate and the pilot will drop out. And all the while the manual reset did not trip. I've watched cooks bang a fry basket on the fryer or kick a door shut and the pilot drops out. Next time your on one tap it with your screw driver. Betchya is opens the limit without tripping it (manual reset).

One way to test them is to check the ohms across the contacts and or the millivolt drop across them.


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Originally Posted by r22coolguy

No, I might have thought that too. Really the pilot staying lit is either the pilot portion of the combination gas valve or the thermopile.

When the pilot goes out can you re-light it right away? Does it go out after the thermostat has satisfied and the main valve shuts off? Does it always shut off during the initial heat up process? You've proved the thermopile is good, really that just leaves the valve.

Now, saying that there is something else you need to check: gas pressure. Hook up a manometer and watch the pressure through the entire process. See if the pilot dropping out is a pressure problem or mechanical problem.


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r22 makes a good point here. The gas pressure is very important, for obvious reasons. One thing to note, the pilot side of the valve comes from the supply pressure, not the regulated side.


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Fry master MJCFSD

Originally Posted by ECtofix

LOL! So Frymaster's factory and world headquarters is WHERE? In Shreveport!

Yeah, Church's Chicken uses them, I'm not sure who else. It's mostly due to the cost I'm sure. A lot of Pitco fryers and such, (simple controls, milivolt, standing pilot) in the restaurants and C-stores I service.

Also, I'm in SE LA and anything above Alexandria is really Arkansas, anyway.

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