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I just slosh the oil around and pull the rope a few times. This has never had gas in it.

I've been thinking about this too although we haven't had a power cut for years and never one lasting for more than two hours, mostly during summer peak load times too. We'd need a 3-phase generator to power the boiler and its auxilliary stuff, there's all sorts of motors connected to it (pellet feed auger etc.). I guess that makes it a diesel unit. If we get it permanently installed we can run it on fuel oil (diesel fuel is taxed much higher than chemically identical fuel oil in most European countries but legal to use in anything stationary). The biggest issue is that we currently have a circulator pump in every apartment so we'd need to devise a way to get backup power into every bathroom. Now if the planner and plumbers had had any sense they'd have installed a system without local pumps and saved us all kinds of headaches.

Even if you figure out how to get generator power to the apartments you'd still have to find a way to keep the residents from tapping into that and adding more loads than just their recirc pump...which would then overtax the generator.

Assuming the circulator pumps are part of the building heating system, not hot water circulation for potable hot water.

Are the circulator pumps for local heat distribution in each apartment? Or, are they to pull building heating water up to each apartment?

If they are used to pull heating water up to each apartment, could they be overpowered by a single higher pressure pump powered off of the emergency generator system feeding the heating plant. Not ideal but would provide heat during extended outages. Motor operated valve(s) would isolate the pump during normal operation.

The pumps operate the central heating in each apartment, a slightly crazy hydraulic setup. Without major reconfiguration I can't see any way of avoiding those pumps. Their power consumption is extremely low though, less than ten Watts, so there might be local solutions.

We're also looking into converting the system to just two central pumps but since the main pipes are severely undersized that might not work.

Does the system not work at all without the small pumps running or does it just not work very well?
You may be able to keep people from freezing during the outages; they just wouldn't be warm and cozy.

My guess that the heating system has a small diameter single pipe central loop that runs from the boiler to the first apartment and then onto the next apartment and the next apartment and so on until the loop returns back to the boiler. Each apartment has two closely spaced tee's that draw the hot water from the main loop and circulates it around each apartment. The boiler's job is to keep the loop warm. Each apartment draws as much heat as it needs from the main loop. Turn off the apartment pump and no heat is removed from the central loop.

Concept is similar to the series connected current transformer driven lights used at airport runways. Each light draws what it needs and no worry about light intensity dropping due to voltage drop.

It's more complex than that. The main loop is a two-pipe system but there is a hydraulic shunt in every apartment that separates the two systems entirely, i.e. without the local pump running everything stays cold because the water in the main loop only goes into the shunt and back into the return pipe. It's a ridiculous setup but apparently the planner (this was only built three years ago) was worried about the pressure drop of the pipework and radiators and chose to split the system using the shunts. The thermostats control the local pumps (on/off).

Potable water is heated using a heat exchanger and another speed-controlled pump in each apartment, basically a tankless water heater minus the burner/electric element.

The whole system is garbage and I'd love to rework it but my uncle (who owns half the house) seems to be happy and doesn't want to change anything. Due to the hydraulic shunts the main pumps always need to run at 100% which makes them awfully noise and the noise carries through the pipes which happen to run right next to my bed. The system runs at 80 degrees C 24/7, heating up the rooms during summer and making everything expensive to run. Moreover, the pumps for the potable hot water are even noisier and the noise travels through the pipes into every single radiator.

A friend of mine is looking into the hydraulic side of the issue and might be able to figure out something affordable but we'll see.

Sounds like a really weird system.
Makes you wonder why some people insist on reinventing the wheel.

Absolutely! Apparently they were worried about the small main loop (restricted by the size of the abandoned chimney flue they pulled the pipes through) so they chose this strange system. Even my HVAC planner friend can't figure out what they were thinking.