Cartridge heater pot problem

I am attempting to control the heat from a 110v 7.1 amp max. Cartridge heater. I purchased a 250 ohm pot resistor which was recommended by a local electronics supply shop. I am attaching one of the heaters two leads to the neutral post in one of our circuit boxes. The other heater lead is attached to the center (of three) lugs on the pot. When I them attach a 110v hot lead to either of the other pot lugs the heater shoots up to its max. heat output and I cannot dial it down using the pot. When I measure the voltage of the three pot lugs, I get 120v at each, no matter the pot knob position. Reading the heater literature it indicates that the cartridge heater output is controlled by voltage adjustment. It does not seem that the pot is functioning. My questions are:
1) Am I hooking up the pot and heater correctly?
2) What is the best way to check the pot for correct function?
Any advice is greatly appreciated, as I am not too familiar with electronics at all. I had this problem dropped in my lap after our electronics guy quit last week.

do you have any pictures of the 250 ohm pot resistor. I hope you have made a mistake describing the pot resistor . IM thinking for that kind of voltage and current over 700watts you should be looking at a variac. There are much better ways to control the heat with SCR's..

Regards Ian

The pot probably fried, though I would have expected it to burn open, but perhaps it shorted out. Either that, or it's not really 250 ohms (perhaps its 250 milliohms). At any rate, you would need one huge pot to do this job. One that can take something on the order of 200 Watts. What you need is some sort of variable voltage supply.

If it's just a simple resistive heater, perhaps a dimmer control would work (like the ones designed for filament lamps). Get one that can handle 1000 Watts or more OR 7.5 Amps or more (assuming that's 110VAC and not DC).

Hi Steve Snap LOL

Hi Ian... I didn't even think of a Variac. That's a good alternative if the dimmer doesn't work. But, once again, that will only work if it's AC and not DC.