Is there a way to turn the furnace off BESIDES the obvious option, the control panel? I know I could use the circuit breaker but that's connected to hot water. It seems like a last resort type thing but I'm about to do it considering I'm up here melting and in a constant battle over the heater. I live with my grandma who has dementia. She constantly turns the heat up way to high and its getting unbearable espcially living at the top of the house.

Heater is connected to Hot water heater? Does your system use the HW heater to supply room heat? There must be a shut off valve somewhere. Can you better describe your HW and heating system?

(Some people mix the words furnace and boiler)

Presuming this to be a boiler & she is actually turning the thermostat up; there are several options. One would be to get a thermostat which can only be adjusted after entering a password. Another is to put a lockable cover over the stat.
I have seen people install a second stat in a hidden location while leaving the original in place, yet disconnected, as a decoy or dummy.

"I have seen people install a second stat in a hidden location while leaving the original in place, yet disconnected, as a decoy or dummy.[/QUOTE]"

Good idea!

The hot water heater is a Rinnai Continuum model 2532 and the Furnace is an Amana High Efficiency gas

The furnace & water heater should not be on the same circuit. Not being an electrician, I can't say for sure but I think each is supposed to be on it's own dedicated circuit.
The suggestions I presented earlier still apply.

Not sure how the two are connected. The HW heater draws a lot of current and is most likely not on the Heater circuit. For the heater, just look for a small valve, normally right next to the heater, in line with the gas supply. Turn the gas off.