Time to install the computer after taking it home to learn Node Red and create the web interface; so I could control the system from my phone via the bus's WiFy network from down in the plumbing bay.
Before starting I made sure the diesel boiler was disconnected, as I only wanted to exercise a few of the pumps (pulled the fuses for the others).
Anyway I plugged the Raspberry Pi back in and let it boot up. All of the sudden all the pumps turned on at once!!! WTF is going on?
It turns out that the relay boards that I brought are Active Low once I figured that out it took less then a minute to change the programming in the function node under Node Red that translates true, yes = 1, false, no = 0 for control of the relays.
In hindsight it would make sense to design a external relay board to not trigger on floating inputs that are not hooked to anything, since we are talking digital signals.
I also had to visit the flow nodes for each pin and set the initialization state to logically high. The area's that I changed are circled in blue in the following picture.
The acid test is reboot the computer and while it is coming up; nothing should turn on, until it is commanded too after the computer is fully functional.
I didn't have the relay boards to test with before hand as I had already wired them up in the bus. So, I simply unplugged the Raspberry Pi and took it home to do my initial learning curve (not much, really easy to use) with Node Red.
During the drag and drop programming; I had verified that each target I/O pin was responding to commands with a multi-meter.
So anyway that quick adventure is over and I went onto the next phase of running another heating test of my DIY hydronic system.
This time I had much less air in the main loop which is the diesel boiler, tanks and distribution manifold and the boiler fired right up and steadily roared away (haven't installed the muffler yet).
Crap I haven't wired in the temperature sensors yet to the Raspberry Pi.
I can feel the pipes getting warmer, crap where is the IR gun? I finally find it under the bus's maintenance manual on the couch and hey the system is already up to 130 degrees, now we are cooking with diesel oil!!!
I should have left well enough alone and continued to monitor it, but hey I am roaming around with the IR gun checking temperatures. With gun in hand, I think hey lets turn on the other zones via the cell phone and verify that the heater cores get hot. Yes they did, but bad move on my part as that injected more air into the system and the diesel boiler shut itself down again.
So hey par for the course two steps forward and one back.
Did some more research and I think I have a solution to the trapped air problem; so time to do some more work.