If it won't switch on from cold, its unlikely to be a thermal switch.
Possibly the switch is failing or possibly the cable is damaged - likely where it enters the machine or leaves the plug. Waggling the cable at the suspect end may show up a fault.
fdsafdsa
October 2017
I can answer this question...
does a multi 20 vac cleaner have a thermal switch?
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Try fixfault.com to fix vacuum cleaners.