because it is simple relay logic. No LEDs, no nothing.
if no codes are showing on a modern NG furnace that is "not working" what components could possibly be faulty?
There can't be too many of them, right?
Here's a good test question:
from this same furnace, on one side of a corroded connection
you measure 24 VAC and
on the other side you measure 3 VAC.
The only load on the downstream side of this connection is your 20 Megohm input impedance DVM.
Without using the ohms range, how many ohms does the connection measure?
In my whole life I've found two connections like this.