Bulb and Capillary Thermostats

Original equipment manufacturers worldwide use thermostat switches designed and manufactured by STEMCO, a Division of Senasys. No matter which style or model you choose, all of the bulb and capillary thermostats operate using the same physics. A fluid is encapsulated in a metal and when the temperature changes the fluid either expands or contracts. This fluid change moves a diaphragm which is in touch with a snap action switch and either opens or closes a circuit.

Commercial food equipment manufacturer’s incorporate Senasys’ high quality, UL approved thermostat switches and control. Other important applications are pool and spa, HVAC equipment and products for the home.

quality ambient compensation

Our capillary thermostats can be ambient compensated to offset the differential in temperature which keeps our thermostat controls more accurate as it’s environment changes.


Senasys takes pride in quality control and reliable operation of our products. Every switch is individually 100% tested before it leaves the plant. Our capillary thermostats are UL & cUL approved.

custom options

Capillary thermostat switches built by Senasys can also be built to customer specifications. This insures you get the exact control you want without paying for features you don’t need.


Products are designed, manufactured, tested and shipped from Senasys’ facilities in Eau Claire, WI to clients across the globe.

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Single Stage Bulb & Capillary Thermostats

Senasys offers a wide range of different single pole, double throw capillary thermostats. Available field adjustable or fixed, the capillary thermostats can be manually or automatically reset.

Two Stage Bulb & Capillary Thermostats

Senasys offers the addition of a second switch (DPDT). The two switches can be a any combination of SPDT auto reset and/or SPST manual reset. 

HYDRASTAT Capillary Diaphragms

The capillary diaphragm assemblies consist of a bulb, capillary tube and a diaphragm. The diaphragm is engineered for a specific movement at a give temperature change. 

Electronic Temperature Switch

The electronic temperature switch is a cost effective, flexible switching solution that allows for tight differentials and tolerances. The digital switch can be used as a standalone board mounted to the control panel, or as a completed enclosure.