Buderus G115 oil boiler question

One of my sons is looking at buying a home with a 5 year old Buderus G115 oil boiler with radiators. When we looked at the home today, the water temp was about 80 degrees. When the thermostat was set up from 65 to 70, the burner ran and the radiators got hot reaching the thermostat setting and shutting down. But the water temp never went over 135. The aquastat was set to 180. I'm used to a boiler maintaining whatever the aquastat setting says but I'm wondering if this boiler operates differently as an energy savings feature. Buderous is a German company and I know they are VERY energy conscious there. Anyone have any knowledge or experience with these units? THANKS!

I think you missed the control system for the 115. It must have an outside temp sensor and the boiler modulation control
that translates the need/ call for heat back to the boiler and that is how the heat level is satisfied. It is likely set as a zero start boiler, and Buderous was one of the first to utilize the 'flexible cast iron' in boilers to prevent damage from the thermal shock of cold returning water. The 115 has a mixing chamber similar to what a Hartford Loop does by blending return water with output water to modulate the temps. No different than what we do with coal stoker boilers, except we only care about uniform water temps, and forget the zero start notion. What brand of burner was on that boiler?

yeah what he said... or maybe the thermometer for the water temp, she no read rite??

Myself and 2 neighbors have Buderus's. They are a "cold start" boiler. They do not maintain kettle temperature when there is no demand. They will only reach the aquastat temp when there is a call for heat, and the temp of the water in the boiler has dropped below the differential. I run my aquastat at 160 in the winter and 130 in the summer. I have a Buderus indirect hot water storage tank for domestic hot water. The tridicator gauges provided with these units are not particularly accurate so this may be why you saw the lower temp. It is possible for the unit to have a call for heat and never turn on the oil gun. The water jacket is insulated and they have a fair amount of thermal mass because of all the cast iron.
The 115 does not have a mixing chamber as whistlenut mentioned. The hot water leaves the top of the boiler and returns to the bottom. The 215 is where they have the mentioned mixing chamber thereby making for a unit that is almost impossible to "thermal shock". Also if the boiler has the Logomatic it will behave differently as well. Myself and my neighbors optioned ours up with typicla Honeywell controls and Riello burners.
My installed costs around 3K materials only. Did the job myself, about 6 years ago.

For $8K you would think it would have an outstanding triadicator.

They are very efficient boilers.

Thanks guys. I think the temp gauge was accurate. I felt the pipe on the discharge side of the boiler and it was about 80 degrees. Just glad to know this is how it is supposed to operate. It did say logomatic on it also. I do think it needs servicing because it coughed and farted when it fired up.

They are a cake walk to clean. The front door with the gun swings open, you can slide out the heat diverters and clean the passageways very easily. The Logomatic is not understood by all service guys but it really operates on some pretty simple concepts.