It is designed as a safety feature in the event that the SSR fails open. By the way you also have an SSR connected to a relay.
If it fails open, then you have no heat.
If it fails shorted (which is how they usually fail) then turn off main power instead of just the heat switch.
If you are refering to a relay in the main power, Its not my drawing. You have to turn power on and off somehow.
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