white = neutral
black = one 115 v leg of 220 V
red = other 115 v leg of 220 V
green = ground for metal case
you must hook up the red leg to get 220 V, you are running on 115 V now. i.e., red to black =220 V
If the heater is designed for 220 Volt, it probably needs all four wired properly to work.
But maybe not the ground, check the instructions.
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