Verified answer

let me compile the good information in these answers

1. top fin, is crap

2. heater is too big . 3-5 watts per gallon depending on climate etc.

3. it may have failed and is overheating because it doesn't shut off

4. it may be fine and your thermometer is bad

5. the room temp may be over 80 and that's why the tank's hot. Is the heater light on a lot ? if so then the heater is heating too much and may be bad, if not, then it 's the room temp

6. some heaters can be re-calibrated, but it's a feature of the heater, EboJager for example can be calibrated, but topfin can't .

Because a 200 watt is for more like a 45 or 55 gallon. You need a 150w, they're a little tougher to find but its the ideal size. The water would then heat probably 76 on minimum and about 82 on max. Anyways, its fine since fish prefer warmer temperatures.

Yeah it's time for a new heater. As someone who likes to tinker with things, I'd be very tempted to try to fix it, but you could end up making it where it over heats, killing the fish, or leaving something open, and electrocuting them, and possibly starting a fire at your socket, so when it comes to heaters best thing to do is replace them!

It probably needs replaced. Topfin heaters only last a few years and then they either overheat or don't heat at all. If its overheating it might boil your fish.

your heater is too big,

for a 36G tank you should only need a 100 watt 55 watt at the min

with heaters never get 1 bigger, smaller can be turned up to match the temp needed, though if you have a bigger one it will heat the water too fast and cook your fish

Replace it just incase they aernt expensive

That is just how top fin stuff works

look for a way to reset it.