Depending on the year, 2010? there is a black switch on the heater. Some, have it on the right side of the heater, others have it just below the control panel. You may also have a failed transformer, or chewed (rats/mice) wiring. Have you taken a look behind the control panel (4 screws) for wire damage?
BTW, yours i beleive is a P-R266A-EN-C