KST200 and KST203 Water Heater Thermostat Guide

What is a KST200 or KST203 Water Heater Thermostat?

A KST200 or KST203 is an adjustable bimetallic thermostat for electric water heaters. It uses a snap-action disc to open or close the heating circuit based on water temperature. Users set the desired temperature via a dial — typically between 90°F and 150°F. The KST200 serves as the lower element thermostat; the KST203 is the upper element thermostat with a double-throw switch.

KST200 vs KST203 What Are the Differences?

Feature	KST200	KST203
Position	Lower element	Upper element
Switch type	SPST (single throw)	SPDT (double throw)
Function	Controls lower heating element	Switches between upper and lower elements
Safety	Basic overheat protection	Built-in high-limit safety switch

Both share:

Voltage: 120/480 VAC

Current: 10A/250V or 15A/125V

Temperature range: 90°F–150°F (32°C–66°C)

Certifications: UL, CUL, TUV, CE

Service life: 100,000+ cycles

How Does a Bimetallic Snap-Action Thermostat Work?

Step 1: The bimetallic strip senses water temperature through tank contact.

Step 2: When temperature reaches the setpoint, the strip bends and triggers a spring-loaded snap action.

Step 3: The snap instantly opens or closes electrical contacts, controlling power to the heating element.

Why snap-action matters: It prevents contact arcing, extends life, and ensures precise temperature regulation without electronic components.

Which Water Heaters Are Compatible?

KST200 and KST203 are direct replacements for Therm-O-Disc 59T and 66T style thermostats. Compatible with: Rheem, A. O. Smith, Bradford White, Whirlpool, GE, Kenmore, Apcom.

How to Install a KST200 or KST203?

1. Cut power at breaker. Verify with voltmeter.

2. Remove access panel and insulation.

3. Label wires before disconnecting.

4. Remove old thermostat.

5. Mount new KST thermostat flush against tank wall.

6. Rewire per water heater diagram.

7. Set dial to 120°F (or required temp).

8. Replace insulation and cover. Restore power.

9. Critical: The thermostat must contact the tank tightly. No gap allowed.

What Is the Global Market Outlook?

The stem-type electric water heater thermostat market (including KST series) was valued at US$2.56 billion in 2024 and is forecast to reach US$3.57 billion by 2031 (CAGR 4.9%). Growth drivers: residential construction, energy codes, and replacement demand.

Frequently Asked Questions

Q: Can KST203 replace a 59T thermostat?

Yes. It is a direct drop-in replacement for TOD-style 59T and 66T.

Q: Is UL certification included?

Yes. KST200 and KST203 carry UL, CUL, TUV, and CE marks.

Q: How long do these thermostats last?

Typically 5–10 years under normal residential use.

Q: Can I adjust the temperature differential?

No. The differential is factory-set between 3.5°F and 16°F.

About the Manufacturer

We are a dedicated bimetallic thermostat factory with ISO 9001 certification and UL E496976 compliance. Annual production capacity exceeds 10 million units. For KST200/KST203 datasheets, samples, or OEM orders, contact our engineering team.