I'm a little confused now. Maybe we are speaking about two different parts, or they make the 1700HD in more than one configuration.
The part in your post #7 is the part I am saying is an overtemp safety sensor intended to shut the unit down it if the heater becomes too hot.
Looks like this: http://www.alibaba.com/product-gs/1447429512/KSD301_manual_reset_thermostat_16a_250v.html
Note the plunger on the top of both parts, used to manually reset it when tripped by higher than limit temp being reached.
Also note the machine stops heating and making fog when this is tripped, until the machine's case is opened and the plunger pressed back down.
In less complex (cheaper) machines an automatically resetting thermostat (no plunger) is used to divert power from the pump until hot enough to fog properly.
If the rest of your machine is working as intended I do not see how the switch I describe would act as you describe. When this switch has opened the heater no longer can complete it's circuit, and can not reheat again until the plunger is manually pressed.
Perhaps you thought I was calling the item you show in post 15 a safety sensor. I think that item is a temp sensor used to tell the unit it is hot enough to fog.
It could be a switch, and if opened might allow the pump to run. But I suspect that won't help you a lot in the long term.