If I plug in a bum thermistor will it kill the board?

Pretty sure I've got a dead thermistor on the extruder. I tested it with an ohms meter using some info from another board member and the ohms meter doesn't move of the original read out. I'd like to power up the v3 to see if a new mega board I installed is working properly, X,Y,Z axis and to see if the print bed and print bed thermistor are working.
If I don't plug in the bum thermistor, will it matter?? Will I be able to get a reading from the print bed thermistor??
I really don't want to screw anything up and I have pretty limited electronics knowledge. This may seem like a simple question, but before I power it up, I'd like to be sure. Thanks

not an expert here but in my imperial experience you have to have a working thermistor in order to turn on the heating element for the extruder, as part of the softwares saftey features. There is probably a way to disable that, but based on your level of experience, I doubt that is advisable,

if you don't want to heat up the extruder, nothing bad will happen from not plugging in the thermistor and functions other than extruding, heating up the element, and reading the unplugged thermistor will work fine...

Edited 1 time(s). Last edit at 10/14/2015 12:54AM by Qdeathstar.

You would risk burning out the the mosfet on the Ramps controller for either the heated bed or the extruder (dependent on which sensor). It isn't worth the risk, the system from memory has protection built in to prevent heating up the elements without a reading from the sensor but lets be honest you can get a sensor for next to nothing on ebay don't risk it. If your multi meter didn't detect any resistance you could check for continuity but my guess is its open.
Grab a new thermistor from ebay and start again.

You can't kill the board with a broken thermistor if the ohm meter doesn't read anything. All you get is a "ERR Min Temp" shown in display.
But you also can't test anything else, because of this error.

I'd look under the shrink tube of the thermistor leads. Usually there is no contact, when the ohm meter reads "open circuit"
The thin legs of the thermistor have to be crimped ( and soldered ) to the connector leads. You might be able to manually make contact and then use tape to insulate the leads.
This is just for testing!
-Olaf

You can leave out the hot end thermistor or use a 100k ohm resistor to check the bed heater, but don't turn on the hot end heater, it will not stop heating, potentially melting the heater block or cause a fire.

Edited 1 time(s). Last edit at 10/14/2015 04:13AM by imqqmi.

Wow! Thanks to all for the answers. I'm skipping plugging in the old (probably dead) thermistor, but will power up the board to check that the motors are functioning (except the extruder motor). Thanks for the advice. I mentioned that I have 5 thermistors on the way, should be here by Saturday. OMT, I noticed that on the extruder thermistor that the actual thermistor is covered by a little collar of metal. The one I placed under the board is not. Does this matter?? Seems like if I tighten the set screw to secure the thermistor in the extruder head, it would break??? Not sure??

If it's a glass bead one, I've crushed a couple of them in the E3D v6. I since switched to a thermo couple and have no issues at all.

A thermistor without brass sleeve shouldn't be screwed in tight.

Carefully push the bead in the hole and secure it by taping or ty-rapping the cable to the heater element's cable.
Make sure the wires aren't shorted by contact with the heaterblock.

Using a thermocouple isn't recommended for beginners. You'd need an adapter board and change the firmware.
-Olaf

I like the clean look of a hot end without kapton tape. Seeing all the problems people are having with thermistors breaking, burning, being off target and the need sonetimes to use a thermo couple as reference, and often beginners need to edit and upload the firmware anyway, I'd say just include it in the kit, include it on ramps 1.5 with converter chip and a pre compiler option to select it in marlin
People can use the thermocouple to check the heated bed thermistor as well, or even create a lookup table automatically, with a few adaptions in the fw. Ymmv