ST thermostat for radiant heater, on/off only?

Hi everyone,

I have a radiant tube heater that currently has an old Honeywell thermostat:

You’ll notice that there are no switches on this thermostat…it’s strictly a line-level switch. No on/off, no heat/cool, no auto/off, etc. It’s wired inline with the 120VAC load side.

I tried a Stelpro STZW402+ but that doesn’t work. I need something that is strictly a thermostatically controlled on/off switch.

Suggestions? Thanks.