Sorry for the delay, the boilers (since I've moved them both into a single chunk) didn't blow up over these past few days but they did reset. I'll be switching to something else. Boiler's are already complex beasts as it is, add in constant resets and explosions it makes the entire process a nightmare. Perhaps the biofuel + generator for the time being. Next up: Powering several nuclear reactors with bees.
Could it be that some part of your charcoal logistics are outside of the three loaded chunks? Being allowed only three loaded chunks seems like a rather extreme limitation, though I will admit I'm not familiar with what is typical for servers.
I've never experienced a boiler reset that wasn't caused by a cut fuel supply, and I usually have a few of them in every world I play. I know, that doesn't help you in the slightest. It's just that my guess would be insufficient chunk loading in this case. If you're the server owner, can you try temporarily making each location (boiler + charcoal + anything else that is relevant) fully chunk loaded (e.g. with a 1-2 chunk margin to the
radius of the chunk loading, 25-49 chunks loaded at each site)?