A fryer thermostat leads a hard life: immersed in hot oil vapour, cycled thousands of times a week, expected to hold frying temperature within a few degrees shift after shift. When it starts to drift or fail, food quality drops first — and safety follows. This guide covers how to specify a replacement (or a thermostat for a new fryer design) and how to recognise when the old one is done.
Temperature range: cover the frying window, with margin
Commercial fryers operate between 50 and 200°C, with most frying done between roughly 160 and 190°C. Pick a control whose adjustable range brackets that working window with room on both sides, so the setpoint sits in the middle of the dial rather than at its end stop. Our AG16-K and AGO series controls cover 50–400°C, which suits fryers and leaves headroom for high-temperature cleaning cycles. Resist oversizing beyond that: the wider the range, the coarser the adjustment at normal frying temperatures and the faster the contacts wear.
Current rating: 16A or 20A?
Convert the element rating to current at your supply voltage. A 3 kW element at 230 V draws about 13 A — inside a 16 A rating, but a fryer element runs near-continuously during service, and heat is what kills contacts. For commercial duty, step up to 20 A whenever the load passes roughly two-thirds of the 16 A rating: the AG16-K is offered at 16 A/20 A, 110 V/250 V, with SPST contacts for a single heating circuit or SPDT when a pilot lamp or alarm shares the switch. For large floor fryers whose elements exceed a 20 A single-pole switch, move to a high-current design such as the AG32-1K (16 A/20 A/32 A) instead of overloading a standard control.
Capillary length and the sensing bulb
The bulb does the sensing, so it must sit in the oil — or in the thermowell in the tank wall — where it reads true frying temperature, not next to the element where it will short-cycle. Measure from the bulb position to the control panel, add slack for routing and service, and order that capillary length; we configure lengths to order. The replacement bulb must match the original diameter so it seats correctly in the well. Route the capillary clear of sharp sheet-metal edges and never kink or crush it: the tube is part of a sealed liquid system, and damage changes the fill volume and destroys calibration.
Always pair the control with a hi-limit
The control thermostat is not a safety device. If its contacts weld, the oil keeps heating. Commercial fryers therefore carry an independent manual-reset limit thermostat in series — our AG16-S trips at fixed points of 380, 400 or 430°C, factory-set for the equipment, and stays open until a technician resets it by hand. If a fryer reaches you without a working hi-limit, fitting one is not optional.
Signs the thermostat is failing
- Oil temperature no longer matches the dial — check with a probe thermometer; drift grows week by week
- Food comes out greasy (oil too cool) or scorches (oil too hot) at the usual setting
- Long recovery after a frozen load drops, or the element cycles erratically
- Dead spots when turning the knob, or no audible click at the setpoint
- The hi-limit trips repeatedly — it is reporting a control problem, not causing one
Replace, don't repair
A capillary thermostat is a sealed unit: it cannot be opened, refilled or re-gassed in the field. Drift beyond a small calibration trim, a damaged capillary or bulb, or welded contacts all mean replacement. Match the old part on range, current rating, contact form, capillary length, bulb diameter and mounting — or send us a photo of its rating label and we will cross-reference it. Browse the capillary control thermostats for 16 A/20 A fryer controls and the safety limit thermostats for the matching hi-limit.