I ran a new 20 amp circuit into my bathroom remodel to supply a 750w wall heater, a bath fan/light combo, a vanity light (3 lamp) and a GFI outlet. I ran 12/2 to the GFI outlet (line side) and then fed the heater, and the light and fan switches with 12 gauge wire off the load side of the GFI. The fan, the heater, and the light on the fan all work great. Before I installed my vanity light, I hit the switch and checked the bare wires at the vanity box for power. Everything appeared fine. When I installed the actual vanity light and hit the switch, the GFI outlet tripped. I pulled the vanity light down and installed an outlet in it's place and plugged in a tester. When I hit the switch, the tester came on and indicated that everything was normal. I plugged an appliance into that outlet and as soon as there was a draw, the GFI tripped again. I was thinking that I could just remove the lights from the load side of the GFI outlet to avoid this, but I wasn't sure if I would be bypassing a potential problem. I'm looking for some insight into why this is happening (I enjoy learning whenever I can) and the proper solution. Thanks for your input in advance!

Wall heater, fan/light, vanity light should all be on line side of GFI. Only thing that should be on load side should be other outlets which are to be GFI protected. Check wiring to vanity light and its switch. Sounds like possible hot/neutral reversed somewhere.

Definitely a problem in how it's wired.
I agree, move the vanity light and heater to LINE side of the GFI. The fan can also be as long as it is not inside the shower area.

I must ask, WHY would you ever consider putting a wall heater on the circuit with everything else? Especially with the receptacle?
Don't you think keeping the heater and receptacle separate would have been a much better idea?

Remove the bulbs from the Vanity and try again, if it doesn't trip now, then likely the Light is being powerd from Line AND Load side.
The Light needs to have Hot and switched leg from Line side OR Load side.
You may have the power to switches not GFI protected, and the neutral from the load side going o the light.
The Load side of the GFI needs to draw equal power on the Load side or it WILL trip.

Agree with Strat. The hot and the neutral have to be taken from the same side of the GFI. Taking hot from load side and neutral from the line side would trip GFI when light tuned on. Would not trip GFI using temporary outlet until appliance is plugged in and turned on. Most likely the fault. Moving every thing to line side would correct the problem. Agree with Stan that you are pushing limits of 20 circuit when you turn everything on and plug in a 1200 watt hairdryer. Plug in a make up mirror you will probably trip breaker. If possible pull a 12/3 cable to box and put heater on separate circuit