My bed stopped heating. (4 replies)

I have a printer of my own design that uses a Rambo controller. It has worked flawlessly for well over a year...until this morning. I tried to do a print and discovered that the bed was not heating. The red light associated with the bed was not lighting. The hot end and all the motors worked normally. I checked the power connections to the bed and found no issues. I went ahead and replaced the bed female power plug just because it had been in service a long tome. Nothing worked. I replaced the Rambo card with another I took out of an older reprap that I knew to be good and the problem persisted.

I think I remember that the thirmister had to be in place for the heater to kick on. It was. I checked the resistance across the thermistor leads and got well over a mega ohm. Is this what I should expect from a cold thermistor? Am I right to assume that resistance comes down as the thermistor heats up? I don't mind replacing it, but that means ordering one and I'm not crazy about waiting a week only to find that's not the problem. There were no changes to the printer prior to this problem. It has been as dependable as sunrise.

Anybody got any suggestions of things for me to look at?