What is up with heat sealers?

Our old one died, got a new one in last night – plugged it in and it worked ok for one bag, so I shut it down – and even unplugged it.

Came in this morning and turned it on and the the unit puts out full heat and becomes too hot to use (melts bags) all over the jaws with crazy heat in less than 3 mins. – even with the thermostat set to 0.

Now waiting for a call back from the company. Even if they send another one it will take 3 days. – this is our busiest weekend with no way to seal our bags…