Beautiful, Philadelphia, the City of Brotherly Love!
I find it easier to first replace every part in the heater, if this doesn't fix the problem then the heater has to be replaced.
Have the exact type of heater installed and you will have spare parts for life, like a lifetime parts warranty.
That is always my advice to customers who only pay for the diagnostic fee.
You don't get paid for the hour. You get paid for the value you bring to the hour. Jim Rohn