As I have found, the thermal switch, in my De Longhi Bambino heater can be re-set manually so that there is no need to buy a replacement. The button is in the back between the two electrical connectors.
To get at it on my Bambino, which may be similar on other De Longhi oil filled heaters, I had to unscrew the foot on the controls side, then two more screws in the metal bit behind and then unhitch the metal bit from a socket near the top.
There's a safety overheat cutout - a thermal fuse - it melts and shuts off the power. As a temporary fix you can "bridge it out" or bypass it by joining its two wires together - buy a new thermal fuse and fit it yourself or have a service person do it for you.
There may be dangers in operating the heater with the safety fuse bypassed - especially if someone covers it with wet clothes.
Do not blame the grandson - unless of course he was given a warning not to do what he did.
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Repair oil heater TRD4 0820T?
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