@Michael 61 Hello and welcome!
How cold are your winters, and how deep is your pond?
@brokensword is right about the depth for temperature differences.
My first winter with my pond, I had a digital thermometer with 2 probes set up: one at the deepest point (around 3 1/2’) and the other just below the surface. No noticeable differences in water temp. We have mild winters here in the Southern US, and even if we get a few days and nights of freezing or below, the water temp stays consistent. I leave my pump going 24/7/365.
Goldfish and koi are cold water fish. They don’t seek out warm water.
Oh, and ditto what
@Tula said. Best to raise the pump up some so as not to accidentally ever have your pond run dry. It’s easier tp replace a burned out pump than it is to replace your beloved fish!