Mechanical Spa Thermostats

Spa Thermostats

Many spas have mechanical thermostats.
Unlike digital or electronic thermostats mechanical thermostats utilize a copper sensor bulb attached to the thermostat body with a copper capillary to measure temperature. The body of the thermostat has rotating dial either located either the side or the top of the unit. This dial is used to raise or lower water temperature to a desired level.
Spas with mechanical thermostats are typically older models & replacing the thermostat can be difficult because the part numbers on an older thermostat may not match up with modern replacements options.  We offer a wide selection of thermostats for all makes of spas here.
If one cannot cross reference any part numbers when trying to replace your thermostat it is important to match up 3 key measurements, capillary length, bulb length & diameter. [see below]

Most spa thermostats are Single Pole (SP) rated at 25 amps with temperature range of 70°F-107°F. 

Here are some commonly found thermostats: 

275-1770-00    1/4"x3.4" Bulb, 22" Capillary, DPDT

275-2535-08    1/4" Bulb, 48" Capillary
275-2568-00    1/4" Bulb, 6" Capillary, w/short leads
275-2568-01    5/16" Bulb, 6" Capillary, w/short leads

275-2720-00    1/4"x3.5" Bulb, 60" Capillary  
275-2720-01    5/16" Bulb, 60" Capillary 
 
275-2950-00    5/16"x2.5" Bulb, 6" Capillary

275-3107-00    12" Capillary
275-3123-00    1/4"x3.4" Bulb, 12" Capillary, Replacement for Cotherm GTLU0025
275-3123-01    5/16"x3.7" B, 12" Cap, Replaces Cotherm GTLU0024 & Brett 34-0121A
275-3124-00    1/4"x3.7" B, 36" Cap, Replacement for Cotherm GTLU0031
275-3124-01    5/16"x4" B, 36" Cap
275-3127-01    5/16"x3.4" Bulb, 36" Capillary, Replacement for Cotherm GTLU3010
275-3136-00    5/16"x6" Bulb, 48" Capillary, Used in Ramco ST-131
275-3142-00    5/16"x2.5" Bulb, 18" Capillary, Replacement for Cotherm GTLU0034
275-3183-00    5/16"x4" Bulb, 48" Capillary, Replacement for Cotherm GTLU0026
 
275-3263-00    5/16"x3" B, 18" Cap, Replaces Hydroquip 3263-00 Cotherm GTLU0016

275-3317-02    5/16" Bulb, 48" Capillary, Found in Patrol & Aquaset
275-3372-00    2.75" - 3.25" Bulbs, Replaces Coates 22002001-55



Thermowell

The sensor bulb is typically inserted into a thermowell, which is a protective fitting that allows the bulb to read the water temperature through the wall of the thermowell with out getting wet. Thermowells come in many shapes and sizes (90° PVC fittings, copper test tube looking fittings & More).
Thermowells are typically found in the foot-well of the spa or somewhere in the suction plumbing between the suction fitting and heater.
The thermowell must never be located after the heater. 
A mechanical Hi limit switch can look like these thermostats & the Hi Limit is attached to the heater - do not confuse the two.

Plumbing PVC Thermowell

Stainless Thermowell

 

Wall Mount Thermowell