I had a heater do that a while back. The built in thermostat is fried. I actually observed mine getting slowly higher over a couple hour period even when it was cranked all the way down.
By the way I don't think that frog looks bloated. He looks well fed. They have the ability to store lots of fat on thier bodies. Mine only get fed 2 times a week because the like the food too much. One of my males is just as guilty as the females too.