Ok, just as a test, connect one boiler at a time to this set up:
Boiler -> Tesseract
Tesseract -> Steam Consumer x2 -> Energy Bridge -> BC Producer -> Conduit -> BC Consumer -> Energy Bridge -> Steam Producer x5
Needless to say, the tesseract is on a dedicated channel.
Steam producers will eat all the power you can give it and it doesn't care one whit if there's a destination for that steam. That makes it the perfect test energy sink as each steam producer will sink 200MJ/t
We're going to test just how much steam the boilers are pushing...
Edit:
All you have to do is check the first bridge to see how much steam is being pulled through the tesseract. If you're not getting what you're expecting and the boiler is definitely at half steam capacity since it won't output steam below 50% capacity, there's something wrong somewhere...
Ok, set this up on single player as my game's server went down as I was starting to muck about.
Set it up and the TL;DR version is, it worked.
One boiler, ~720. Two boilers ~1.4k. 3 ~2.1k. In and out. As it should. And, not like it was on the server.
Or was it? That set up was using BC producers/consumers. Went back and swapped them for HV like I'm using on the server with all 3 boilers on line and everything except the energy being made the same and.... 1056. Added extra connections between the HV Producer and Consumer, no change, 1056.
So the HV producer is the limit. Swapped out the HV for EV and it was back to using all the steam again with ~2.1k out the other side.
Brought it up to 5 boilers and the EU/t was running 1.7/1.8k fluctuating with 3600 steam on the far side, max output for the 5 boilers. Both with all Tesseracts on the same frequency and with each boiler pair matched to one on a consumer, same result.
Of course, the max per consumer is 1000, so added 2 more boilers for a max boiler out of 5040 with 7. And the result was that the max it will handle to make the full EV amount of 2048 is 4215 mb/t, so you only need 6 boilers to get to that. Will put an HV transformer in line after the EV producer to get 4 packets of 512 EU/t for each tick of 2048 EU.
Swapped back the BC producer/consumer with all 7 pumping in and it maxed out the bridge, all 5 faces at 1000 steam each and outputting 1000 MJ/t
Oh, and FYI, didn't need 5x Steam Producers on the other end, all the steam was pumped out of one side (down).
Thanks for the idea, it set me on the path to figure out the issue was the HV Producer. (Really hoping that wasn't an obvious bit of info I overlooked. My Google Fu is normally strong... )