Other thing to check.......Are you measuring the voltage across the signal portion of the SSRs? Ie: Looking for voltage changes when the PID is turning them on and off? If they're not getting any change in voltage, then something is wrong between the PID and the SSR. If they're getting voltage changes, but in turn the SSR is always on, then its a bad SSR.
Finally, measure the amps/watts you're getting at the element. If its full power, then its something upstream at the SSR. If you're getting 1/4 the power, then its an issue at the contactor and contactor is open and you're getting power from the hot leg that isnt connected to the SSR