Fun stuf eh?
The brown unit is a wood fired boiler. The exposed terminal is the 120V side of a transformer for a zone valve that opens when the wood boiler is up to temp. Yikes!
The valves on the back are the zone valves for the baseboard heaters. The yellow wires with all the wire nuts are 28V circuits going to the zone valves. The wire plugged into the outlet is connected to the transformer that supplies power for the circulating pump and the 28V for the zone valves.
The big tank is actually a hot water heat exchanger storage tank. There are no elements in it. Just a coil that is connected to the boiler. But the TPR valve has no extension on it. Now, would it ever get hot enought to lift it? I don’t know. But if it has a TPR valve, I think it needs an extension!
I had the water tested. No results from the lab yet, but is is from a sand point and has a lot of iron in it.
The stuff on top of the wood boiler is a replacement zone valve that hasn’t been installed yet.