Bathroom on one 20 amp breaker is code. Sounds like you have a faulty fan.

The fan does not have to be GFCI protected unless it is in the installation instructions.

The fan likely has a defect.

I should have mentioned that the fan is not gfci protected. The gfci is on same circuit as rest of bathroom but is pigtailed and doesn't control anything else

The fan is on the LINE side of the GFCI?

Sounds like someone hooked some neutrals together incorrectly.

Other devices on the line side of the GFCI should not have any effect on the GFCI if all the wiring is correct.

thanks for the help. but sounds like a job for a pro.

With a DVM and an incand. lamp you can very likely check whether the GFCI is tripping for valid reasons, but the default fix is to replace the GFCI.

I will change the gfci first, and then the fan motor if there is still a problem. Is it o.k. that the gfci and exhaust fan are sharing a neutral?

both the neutrals have to be on the line side of the G.F.C.I.

both the neutrals have to be on the line side of the G.F.C.I.

To elaborate: There needs to be THREE neutrals. The feed from the circuit breaker has one, the exhaust fan has one (those should be connected together either and to the LINE side of the GFCI). Any GFCI protected loads have one and that should be connected to the LOAD side. Nothing form the protected side (hot or neutral) should touch anything on the line side. Also make sure that none of the neutrals touch ground anywhere (other than back at the disconnect).

thanks ronnatalie for explaining. the wiring is just as you say it should be. looks like I have a bad gfci

If the GFCI can be reset and everything else works untill you turn on the fan, I don't see how it could be the GFCI.

If the above statement is true then the GFCI is doing its job.

I installed a new gfci and has been working fine since. Thanks for the help