[Myka]

For $3, why not get a new thermometer? It would be very odd that you have 3 heaters that suddenly are stuck on. Have you confirmed that the heaters are getting warm? Just because the light is on doesn't mean it's working properly. I've had this happen recently. Light came on, but element didn't get warm. Is all your other equipment working fine? There was no surge in your power or something?

You can calibrate Jager heaters by lifting the blue "knob" on the end of the dry end. It takes quite a pull to lift it, then you can move the numbered dial around without changing the setting on the heater. I have a feeling that you've been messing around with the heaters' dials a lot and they are just all whacked out now.

You say the light stays on even if at the lowest setting? If I were you I'd get out a 5-gallon pail, fill it with tap water at 78 degrees (or close to the temp you want tank to be, don't fuss too much). Put one heater in the pail, turn it down to the lowest setting, come back in 20 mins and see if it's still on. If the light is on, pull the heater out and check that the heater is actually warm. If it is indeed overheating the bucket of water, lift the blue knob, turn the numbers so it's now at the highest setting, push the blue knob back in, and turn the heater down more. Do this a few times and see if you can get the light to go off and the element to stop heating. You can have a pail for each heater if you want, but only have one heater at a time in a bucket.

Also, sometimes it takes a few minutes, maybe 10, for the heater to adjust to the new setting, so wait at least 10 minutes before adjusting it again, but better off waiting an hour or so and checking the temperature on the thermometer rather than going by the light indicator.

FWIW, I use two heaters in each tank. I have 2x 100W Jagers in my 50-gallon + 30 sump.