We just got a new propane heater for our swim spa and my dad installed it. He is not a licensed electrician, but he has done a little wiring on different things. Besides the price was right. We did not realize after removing the old heater that its wiring was 240V so we installed a GFCI outlet using the old heaters wiring thinking it was 120. When I plugged the new spa heater into the outlet I heard a loud pop and then nothing. My question is what would have popped when I plugged the 120 power cord into the 240V wired outlet? We have since read the manual and removed the power cord and hardwired the heater to its own circuit breaker using the 240V wiring. The heater we purchased could be ran as either 120V power cord or hardwired 240V. I would really appreciate any help I could get. Thank you.