I'm not an expert but;
1. Its probably not the igniter. If it were the furnace would start up normally with the draft blower, than power up the igniter ( which is dead but the furnace wouldn't necessarily know this yet), then open the gas valve. After a couple of seconds the furnace would realize that there was no flame because the photo eye would not see anything and cut the gas. This triggers an error code on the red led.
2. The circuit board is probably powered by 120 volts and has its own step down circuitry separate from that of the tstat . I suspect the circuit board is supposed to generating the 24 volts for the tstat but no longer is. If thats the case you are looking at a new control board. Still its probably worth a look to see if there is a separate 24 xformer off of the incoming 120v line. If there is you may be in luck.