amplifier IC. The IC contains four built in totally independent operational amplifiers and in this circuit we have used all the four opamps of the IC. Each opamp is operated separately with a relay on its output. A separate variable resistor is also used with each opamp to select a desired temperature point on which its output relay will be activated. For example to adjust the activation point of relay1 adjust VR1, to adjust activation point of relay2 adjust VR2 and so on. A 10K thermistor is used in the circuit to sense the temperature.

The circuit can be operated from 5V to 12V DC. Relay values should be selected according to the operating voltage. For example if you are operating the circuit with 5V then use a 5V relay and if you are operating it with 12V then use a 12V relay. 

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Here is a project of a four level temperature controlled switches. At the output of the circuit there are four relays, each relay will be adjusted to activate on the desired temperature and a separate device or appliance could be connected with each relay.
The circuit is build around a LM324 quad operational
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Four Level Temperature Controlled Switches