Help with dead furnace

I'd appreciate any advice any of you can give me

Last week I had my electrical service upgraded to my house, by which I mean I had the electric meter replaced and put in new cabling into the breaker box. I also had a new ground rod installed because the house previously hadn't been grounded (I assume the ground was done through the water pipes. To do this the power company turned the power to the house off for a few hours, and then back on again.

But when the power came back the furnace was dead. Nothing at all happening.

Adjusted the thermostat, replaced the batteries in the thermostat, nothing. Took the front panel off and power cycled the furnace (with the safety switch activated manually) and the LED on the control board stayed resolutely off.

So I figured the control board might have been blown by a power spike when it went on, so I went out and picked up a new one, installed it by mapping all of the wires over from the old board to the new and turned it on, and there was nothing. Still no LED response, it just stays off.

Then I became a bit more methodical and went through and tested the entire electrical circuit with a multimeter:

Started with power at the switch next to the furnace (there is no fuse there), 120V no problem there

Then tested the microswitch on the door - again no problem, worked fine - 120V hot when the circuit was closed and zero when open.

Bypassed the thermostat by connecting the terminals directly

Checked the fuse on the new controller board (the old one didn't have one)

Tested the connection to the new controller board:

120V hot input on the correct "line in" terminal, and 120V across the hot and neutral 'line in'. It is possible that the neutral and ground have been mixed up back in the breaker box when the service was upgraded, but I don't know how to check that, and I'm not sure that it would make much of a difference. Checked that the polarity is correct and that hot and neutral haven't been switched around (although there is an LED error code for that so even it it were the problem the board should tell me)

120V output to the transformer, and checked that 120V arrives AT the transformer. Checked that the transformer's pushing out 24V and that this is getting back to the control board.

Checked the start capacitor for the blower motor and it's capacitance is fine.

The only thing I haven't checked is the electronic ignitor (or the thermocouple - I assume that even if it was dead it wouldn't affect the startup of the control board).

What am I missing? What else could possibly prevent the control board from at least trying to boot?

The furnace is a Armana air command high efficiency 90

The original control board is a White and Rogers 50A50-206 which was replaced with a White and Rogers 50A55-843 which is apparently the new correct replacement part

Before I swallow my pride and call in a pro if there's any thing you can think of that I have missed it would be hugely appreciated.

submitted by /u/imtotallystumped
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