Plastic doesn't require tevila but metal does (d'oraita according to many, see OU here under A). As such, if the metallic resistor touches the water (and I assume it does) then you need tevila with a blessing.
On utensils made of metal and plastic, kashrut.com (on top, letter b) writes
A utensil made of a material requiring tevilah should be immersed
inclusive of any plastic or wooden parts attached to it. A utensil
made of wood or plastic requires tevilah if any metal is attached to
it, providing that the metal touches the food and is vital for the
utensil’s use. A utensil made of separable parts requires tevilah only
for its metal parts.
The OK writes
Electrical equipment that comes into direct contact with food requires
tevila – for example, if one has an electric water urn, electric hot
plate or popcorn maker, one needs to toivel at least the parts (if
they come apart) of the equipment that touches the food. The wire does
not need to be toiveled. (Some poskim hold that the wire should be
toiveled.) It is preferable to wait a few days until the appliance is
completely dry after it was toiveled before using. If one is concerned
that it may get ruined, one should discuss this matter with a rov.
Kashrut.com here says the same for a pyrex kettle and practicalhalacha here for a tea kettle.
For more sources see Kof-K bottom of p. 5.
And as always (thanks Ezra for the reminder), don't trust what strangers write on the Internet and ask a rav for practical rulings.