My blower motor will not stop running,and my ignitor doesn't light.

Are you saying the blower motor would run intermittently and then just stopped working? My first thought is faulty blower motor, I've seen faulty blower motors that would run intermittently. Any motor that uses brushes, you can tap on the motor to see if it will start working, that is a sign of bad motor brushes, replace the blower motor. There could be other issues?
Did you check the blower fuse, not only check the fuse, check the fuse circuit for voltage, use a test light. Check for applicable hvac trouble codes. With hvac on, check for voltage and ground at blower motor wiring connector, if both are good and no blower action, suspect the blower motor.

This is a down flow unit. There is no pressure valve on this unit. Here is all the parts on this unit.
1. Manual - reset, when used.
2. Blower and blower motor
3. Relief box also known as a exhaust flue.
4. Gas valve control knob or electric switch, ON/OFF
5. Gas Valve
6. Gas burner
7. Ratting plate
8. Blower door safety switch
9. Blocked vent safeguard tube and switch
10. Gas Manifold
11. Manual limit switch (2)
12.Hot surface ignitor
13. Flame sensor
14. Inducer blower motor
15. Control board with relays and transformer.
That is all the parts. The first thing the heater gets a call from the thermostat to the control board marked W. The board sends 24v to the inducer fan relay which makes and causes the inducer fan to come on now there is a small tube that runs from the inducer fan box to a switch when the switch makes it sends power to the board which proves you have cleared the exhaust flue then the flat surface ignitor starts to glow and then gas valve opens and fires. now if this tube is stopped up the heater will not fire and will lock the unit out. Also if the flue is stopped up with trash it will do the same thing. If you are not familiar with gas heating units you should call a service company out and check out the system there is a lot of things that need to be checked out every heating season as to keep you and your family safe.

DISCONNECT THE BLOWER MOTOR POWER LEAD. RUN A "FUSED" (20AMP) HOT JUMPER WIRE TO POSITIVE SIDE OF CONNECTOR,THEN TO BATTERY POSITIVE, THEN RUN A NEG. WIRE BACK TO NEG. AT BATTERY (TO INSURE A FULL CIRCUIT).
IF BLOWER WORKS...YOU HAVE A SWITCH,WIRING, OR FUSE/CIRCUIT BREAKER PROBLEM.NEXT CHECK FOR POWER INTO BUT NOT OUT OF SWITCH...IF THIS IS THE CASE THE SWITCH IS THE PROBLEM.

Do you have the model number? There is a problem with either the blower motor sensor or the ignitor. When the furnace get a signal for heat, the blower motor comes on and then the ignitor. If either one of those fail then it stops, waits and tries again. When the tech was there, if he did not replace any parts then he did not do his job. You can call them back out because the issue was not resolved or you can post the model number for us.

With the blower turned on, try tapping the blower motor with something hard. If it restarts, then this is a failing motor. If it doesn't start, then check power to the motor. If it has power, then the motor has failed completely.

usually a "humming motor" indicates either a bad capacitor or a defective motor. With the power off try to spin the blower wheel...it should spin freely. If it is tight or wont spin and there are no obstructions stopping it (like an air filter sucked into blower or other debris) then the motor most likely is seized. If the blower wheel spins free then you may have a bad capacitor. Keep in mind, just because the blower spins easy doesn't mean the motor is good. I have had motors that are defective that dont seize up but most of the time the blower wheel will not spin free if the motor fails.

Change the. Blower motor resistor. $25 part near the blower. Chevy suvs are famous for bad blower resistors

Being a Plymouth,I would look at the fan switch in the dash,bet it doesn't look ok !!

check blower motor and resistor with test light,