About half the lights in my house went out after I changed the light bulb on a "tricky" fixture. I found the tripped breaker and flipped it back on. Now all of the lights will come on, EXCEPT the "tricky" one, which seems to have been the source of the initial trip. What should/can I do? Is this a serious problem?
You need to test the voltage between hot and neutral at the light fixture and also going back along the route of the circuit back to the panel. Be sure that the breaker in question also has the 120 volts hot to neutral (for breakers the neutral is over on the terminal strip where all the white wires come together).
The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.