Help with Peerless FlexHeat Boiler

Hi all,

Thanks very much for reading.
We inherited this fancy setup of Peerless FlexHeat hot water boilers on natural gas, controlled by a Tekmar 268 boiler controller. These boilers supply heating and hot water.
Each of the boilers has its own circulator pump.



This will be the first cold season that we're looking after these boilers.
When the heating kicked on during a cold week (a couple of weeks ago), I noticed that the middle boiler did not turn on. Pressure gauge shows 0, pipes are cold, no gas or flames underneath including pilot.

I downloaded the manual for the Tekmar controller, and ran some tests, also set to Max Heat.

The middle boiler still did not turn on or show any signs of life.

I removed the front covers of all boilers.
First observation was that the middle boiler's gas valve had all this strange white/gray dust on it, and the gas pipes connected to the valve had much more exterior rust than the other boilers.

The box on the right top inside the boiler looks like the pressure control unit. There was current on both poles.
I checked for electricity on the wires inside the boiler and there seem to be electricity running.
There was no smell of gas. The circulator pump for the middle boiler was cold.

For now I shut off the gas and electricity to the boiler, and all the ball valves leading water to/from it.

I suspect the gas valve.
But I'd greatly appreciate help with diagnosing the issue.