So I'll lower the temperature of the system's water today, that should make the boiler go for longer with a smaller flame (plus the 100W water pump will be on longer, too
). I've wondered about replacing the burner with one from a smaller model - that way the boiler would be working at higher load (higher efficiency?) to keep the same temperature. In the spring I'll ask the maintenance guy about that.
A good side of lowering the water temperature in our system is that the radiators and pipes won't expand and contract as much (I can hear them creaking and whining shortly after each time the boiler fires up). This may help keep the 40 year old system from springing a leak or two.
On the other hand, with the system at a lower temperature there will be less heat radiating, so I might be forced to raise the thermostat's temperature a bit to stay comfortable.