A fryer that shuts itself off in the middle of service is usually reported as “the thermostat is gone”. Most of the time the device that stopped it was doing its job. This page is the order of checks worth running before buying anything: what each device actually does, which symptom points where, the three faults that imitate a failed part, and — if it really is the part — the five dimensions that decide whether a replacement is safe.
In a commercial gas fryer the word covers three parts that do different jobs, and the difference is the whole diagnosis.
The regulating thermostat senses oil temperature through a bulb and capillary and cycles the gas valve to hold the setpoint. When it reads low the oil overheats; when it reads high the fryer underheats; when it sticks it stops cycling at all.
The hi-limit is not a temperature control. It is an independent safety cut-out set above the operating range, wired in series with the gas valve. It opens when the oil gets hotter than it should and, on a manual-reset model, stays open until someone presses the button. Its only job is to stop the fryer before the oil reaches ignition territory.
The thermopile makes the millivolts that hold the gas valve open. No pilot flame, no millivolts, no gas — and nothing the thermostat does will change that.
So the useful first sentence is: if the fryer shut off at a temperature above the setpoint, the hi-limit worked. The question is not why the hi-limit failed. It is why the oil got that hot.
| What the fryer does | What it usually means | Look here first |
|---|---|---|
| Cuts out mid-service, will not restart until a button is pressed | A manual-reset hi-limit latched | The over-temperature cause, not the hi-limit itself |
| Cuts out, then restarts by itself once it cools | Auto-reset hi-limit, or a control cycling on a cold reading | Bulb, well, control |
| Never reaches setpoint; flame goes out shortly after lighting | Millivolts or gas valve | Thermopile, pilot assembly |
| Oil runs far hotter than the dial says | Thermostat reading low | Bulb seating, fouled well, wrong part |
| Trips again within minutes of resetting | Genuine over-temperature condition | Heating left on, control welded, blocked flue |
The table is coarse on purpose. It exists to stop the most expensive move in this repair: buying the device that reported the fault instead of the device that caused it.
If you have already replaced the thermostat, the hi-limit or the thermopile and the fryer still cuts out, stop buying parts. Three conditions produce exactly this symptom, and none of them is the device you just changed. In the service threads below this is the single most common way a repair goes wrong twice.
1. Low oil level. The bulb and the hi-limit probe sit near the bottom of the vat. If the oil is below them they read air, not oil — the thermostat sees a cold load and keeps calling for heat while the oil that is present keeps climbing. Top up to the marked line and the “fault” often disappears.
2. A fouled bulb or well. Carbon and polymerised oil insulate the sensing bulb. It now reads lower than the oil actually is, the control compensates by heating longer, and the oil temperature climbs until the hi-limit stops it. Replacing the hi-limit in this state gives you a new part and the same fault on the next shift.
3. A control calling for heat continuously. A welded contactor, a stuck relay or a probe reading cold keeps the valve open regardless of what the thermostat is asking for. On electric fryers the equivalent is a contactor that does not drop out.
All three share a signature: the hi-limit trips at a temperature where it should, and the oil genuinely was too hot. The part is not lying to you.
With the fryer isolated and cold:
Gas valves, pilot assemblies and 208–480 V elements are not bench items. Isolate power and gas, and treat anything on the gas train as licensed work.
| What must match | Why it matters | What goes wrong when it does not |
|---|---|---|
| Cut-out temperature | It defines the protection limit | A higher setpoint means the device no longer protects the oil |
| Reset type: manual vs automatic | Manual latches a fault; auto recloses when cool | An auto-reset in a manual application lets the fault repeat unattended |
| Capillary length | Routing from the vat to the control | Too short cannot be routed; too long coils against a hot surface |
| Bulb or probe dimensions | Seating in the sensing well | A bulb that does not seat reads low and the fryer runs hot |
| Fitting and thread | Mechanical attachment to the vat or well | Will not mount, or mounts without sealing |
Interchange tables, including the ones compiled on this site, are claims about compatibility carried over from distributor catalogs. They are not verification. If a listing does not state the dimensions that matter, it has not been verified at the level that matters.
None of the failure modes above announce themselves as “wrong part”. They look like a different fault or, worse, like nothing at all.
The cost of a wrong safety device is not the price of the part. It is the second service call, and the thing that did not happen when it should have.
A diagnosis that ends in a part number still needs the numbers that decide fitment. These are the records on this site that cover each device, with the values printed in the source tables — not measured here, and not averaged across variants.
| Device | Record | Published values that decide fitment |
|---|---|---|
| Control thermostat, RX | 00-411506-00013 | 200–400 °F; capillary 24 in; bulb 3/8 in × 5-5/8 in; 3/8 in MPT stuff box |
| Control thermostat, KX | 00-410687-00001 | 200–400 °F; capillary 48 in; bulb 1/4 in × 12-1/8 in |
| Control thermostat, K | 00-414880-00001 | 200–400 °F; capillary 96 in; bulb 5/16 in × 8-1/16 in |
| Control thermostat, Fenwal | 00-348361-00001 | 75–550 °F; probe 4-3/4 in; 1/2 in NPT |
| Hi-limit, manual reset (LCH) | 00-414146-00002 | cut-out 435 °F fixed; capillary 24 in; bulb 1/4 in × 4-7/8 in |
| Hi-limit, auto reset (LC117) | 00-419670-00001 | cut-out 450 °F fixed; capillary 30 in; 3/8 in MPT stuff box |
| Thermopile, coaxial | 00-348358-00001 | 250–750 mV; lead 36 in; 3/8-32 thread; 1 pole |
| Thermopile, two-lead | 00-410839-00004 | 500 mV catalog figure (band 250–750 mV); lead 36 in; 2 poles |
| Gas valve, millivolt GHF | 00-410841-00001 | 3.5 in WC NG; 0.5 psi max inlet; 300,000 BTU; 3/4 in FPT |
| Gas valve, 24 V | 00-410841-00028 | 24 V AC 60 Hz; 14 in WC max inlet; 300,000 BTU; regulator setting not consistent across sources |
Two things follow from the table. First, the same “200–400 °F” control exists with a 24 in, a 48 in and a 96 in capillary: the range is not the identity, the capillary is. Second, the two hi-limits on this site differ in cut-out (435 °F vs 450 °F), reset type and capillary (24 in vs 30 in) — a substitution across them changes the protection limit as well as the fit.
Where a figure is contested between sources, the record says so instead of picking one. The 24 V valve regulator setting is the current example: 3.0 in WC in one catalogue, 3.5 in WC in another. A reference that hides that disagreement is less useful than one that shows it.
This site compiles part numbers, dimensions, cross-references and published specifications so that identification takes minutes instead of an afternoon on hold. It does not certify fitment, does not sell parts, and does not quote availability.
Verify any number here against the equipment's own parts manual before ordering, and have gas-side and safety-device work done by a licensed technician. A reference is a starting point, not a substitute for the manual.
Each claim above is backed by one of these lines, quoted as published. Where the source is a distributor rather than the manufacturer, it says so.
| Document | Wording (verbatim) | What it settles | Link |
|---|---|---|---|
| PartsFe specification for 00-414146-00002 (distributor wording, not OEM) | “Hi-Limit Type - Lch W/Manual Reset · Temp 435 Fixed” | A manual-reset device is the one that stays open until someone presses it — the fingerprint of an over-temperature event. | partsfe.com |
| PartsFe specification for 00-419670-00001 (distributor wording, not OEM) | “Hi-Limit Type - Lc117 W/Auto Reset · Temp 450” | An auto-reset device closes again on its own, so the fryer restarts and the fault repeats — which is why 'it keeps tripping' can mean either device. | partsfe.com |
| Vulcan-Hart, FORM F-37136 Rev. A (January 2024), LG Series Fryers | “00-410840-00002 High Limit” | The OEM catalog treats the high limit as its own line item on the control panel, separate from the thermostat kit beside it. | www.webstaurantstore.com |
Compiled from OEM parts manuals and distributor catalogs for the part families indexed on this site; the check order reflects the standard fault sequence used in commercial fryer service literature (low oil, sensing error, control, then device). Dimension and setpoint values are reproduced from the source tables, not measured. See Sources & method.
Underlying dataset (CC0): DOI 10.5281/zenodo.23613054