Geyserwise Smart Life Ptc?

[Islay]

In using the Smart Life app I note the following settings on the geyserwise applet:
Ptc: on/off
Ptc temp : 75 Deg C
What does this stand for, what is its use?

 

[Speedster]

In using the Smart Life app I note the following settings on the geyserwise applet:
Ptc: on/off
Ptc temp : 75 Deg C
What does this stand for, what is its use?

It is a positive temperature coefficient element.