Technical guide

How to Choose the Right Thermostat

With sixteen models spanning −45 °C to 425 °C, 12 V DC to 250 V AC, 6.3 A to 45 A, and automatic or manual reset, selecting the correct Thermorex thermostat can be daunting. This buyer guide breaks the decision into five steps: temperature range, voltage and current, reset type, contact configuration (NC vs NO), and mounting method. A quick-reference table maps every model to its key parameters so engineers can shortlist candidates in minutes and request a factory-calibrated sample for the exact set point needed.

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Certified vs Counterfeit: The True Cost of a €1 Thermostat

A commodity KSD301-class thermostat optimises for unit price; a certified device optimises for a predictable, documented failure mode — the entire point of a protective component. This guide breaks down where the savings come from, why counterfeit certification marks are widespread at the bottom of the market, how to verify a mark against the certifying body's register, and how to migrate from a commodity part to a certified, factory-calibrated equivalent such as the TK24, TK77DC, or TK224.

TK24 or TK24HT

TK24 is a versatile ½-inch thermostat that handles higher currents (16 A/10 A) up to 200 °C, with contacts configurable to open or close on temperature rise and IP64 sealing when required. TK24HT trades current capacity for extreme-temperature endurance, surviving to 425 °C with a fixed “opens-on-heat” contact scheme, ±6 °C tolerance and IP4X protection. In short: choose TK24 for mainstream 200 °C duty with better sealing, and TK24HT for high-heat safety cut-outs where lower current is acceptable.

Parameters overview

This reference piece walks through 14 critical parameters—rated voltage/current, temperature range and hysteresis, cycle life, insulation strength, IP rating, power factor, and reset style—that govern a bimetal thermostat’s safety, accuracy, and longevity. Each parameter is defined, its design impact explained, and typical values given (e.g., ≤250 V, 100 000 cycles, ±3 °C tolerance). Taken together, the list serves as a designer’s checklist for matching a thermostat to demanding consumer or industrial applications.

TK32 or TK32OS

Both TK32 limiters break the circuit between 30 °C and 250 °C, but TK32 resets manually after cooling while TK32OS is a one-shot device that stays open permanently. TK32 therefore suits equipment that a technician can inspect and re-activate, whereas TK32OS guarantees a non-restartable shutdown in fire-safety, medical, or chemical systems. Accuracy is similar (±3 °C/±6 °C), so the decisive factor is whether the application must allow or forbid reset.

Variants of TK34

The TK34 family shares a bimetal disc core and full customisation, yet differs in reset mode and current rating: TK34A is automatic-reset and carries up to 45 A; TK34R adds an internal heater for faster, targeted switching up to 25 A; TK34M requires a manual reset and handles 40 A for safety-critical scenarios. All models cover roughly –25 °C…120 °C and exceed 100 000 cycles at moderate loads, making them drop-in solutions from consumer heaters to industrial motors. Selecting the variant is essentially a trade-off between hands-off convenience, response speed, and the need for operator inspection.

TKP or TKPCS

TKP and TKPCS are shaft-adjustable, automatically reset thermostats rated up to 16 A and 250 VAC, but TKP offers finer tolerances (±3 °C…±10 °C), reset offsets from 5 °C to 15 °C, and operation down to –45 °C. TKPCS adds current sensitivity, uses dual “Low/High” tolerance bands (±20 °C/±10 °C) with a fixed 15 °C reset, and has higher contact resistance (0.15 Ω) that is acceptable in power-regulation roles. Engineers pick TKP when tight thermal control or sub-zero service is paramount, and TKPCS when load-dependent trip behaviour and simpler calibration are more valuable.

Referenced hardware

Products these guides cover

Every certified TK-series family is configurable to your exact set point and built to order.

-45…200 °C

TK24

1/2" bimetal switch that responds to temperature rise or fall used to maintain a desired temperature between two designated values.

200…425 °C

TK24HT

1/2" bimetal switch for high temperatures used to maintain a desired temperature between two designated values.

30…250 °C

TK32

1/2" bimetal temperature limiter with manual reset which is dedicated to prevent overheating disconnecting the circuit.

30…250 °C

TK32OS

One-shot 1/2" bimetal temperature limiter which is dedicated to prevent overheating disconnecting the circuit.This is device is working as thermal fuse.

-40…170 °C

TK77DC

3/4" bimetallic thermostat that responds to temperature rise or fall used to maintain a desired temperature between two designated values.Dedicated for switching DC load.

30…190 °C

TK124

Bimetallic temperature sensitive switch or cyclic operation device with automatic reset control - blade thermostat.

30…200 °C

TK127

Bimetallic temperature sensitive switch with 12,7 mm size with automatic reset control. Ceramic body miniature thermostat.

-25…190 °C

TK224

3/4" bimetal two-pole switch that responds to temperature rise or fall used to maintain a desired temperature between two designated values switching automatically on off 2 pole of electrical circuit.

50…190 °C

TK232

3/4" bimetal two-pole thermal limiter that responds to temperature rise used to prevent for overheating device. This temperature sensitive element automatically switching off 2 pole of electrical circuit.It is not self regulating - requiring manual reset for safety reasons.

-45…250 °C

TKP

Adjustable thermostat TKP family is a temperature-sensitive switch that controling set temperature by automatically switching the power supply on or off. This is dedicated to heating and colling systems withvarious if options.

-45…250 °C

TKPCS

Adjustable thermostat TKP family is a temperature-sensitive switch current sensitive that controling set temperature by automatically switching the power supply on or off. This is dedicated to heating and colling systems with various if options and it can be used also as regulator of energy.

-25…120 °C

TK34A

3/4" bimetal switch that responds to temperature rise or fall used to maintain a desired temperature between two designated values switching automatically on off of electrical circuit. This thermostat can be used in high current applications (up to 45A )

50…120 °C

TK34M

3/4" bimetal thermal limiter that keeping to temperature under set value preventing for overheating the circuit. After actuation it is required to manual reset.This thermostat can be used in high current applications (up to 45A )

-25…120 °C

TK34R

3/4" bimetal switch that responds to temperature rise or fall used to maintain a desired temperature between two designated values switching automatically on off of electrical circuit.It Internal resistance heater included.This thermostat can be used in high current applications (up to 45A )

-30…180 °C

TK-AA-01

Bimetal hermetic temperature sensitive switch or cyclic operation device with automatic reset control

-30…180 °C

TK-AA-02

Bimetallic temperature sensitive switch or cyclic operation device with automatic reset control