The "PLT" error code means pilot failure. The lack of spark may or may not mean an ignitor problem.

I have seen the "PLT" code come up because the main valve in the heater was in the "off" position. No gas = no pilot. Have also seen clogged pilot-burner orifices. The lack of spark may have to do with water flow issues (dirty filter, clogged basket, etc.), or it may be a problem with the electronics of the heater.

All of these (except turning the gas valve on) will require a competent service tech to diagnose.