I replaced the HSI today and it still doesn't seem to be working. There is a solid red light that begins to flash when the HSI fails to heat up. The blower seems to be functioning properly and the furnace won't begin operation until it the set temperature exceeds the room temperature ruling out the thermostat. Any body have any advice?

Verify that the HSI is getting powered. This will require a voltmeter. Connect the probes to the harness plug & start a heating cycle. If you do not read 110-120 volts during the ignitor warm-up trial, the circuit board is likely the problem. Also check the continuity of the HSI harness between the plug and the board.

P.S. The blinking light should provide a clue. Look for a label inside the blower access panel with a fault code legend. The ignitor may not be the problem at all.