on numerous occasions. Bear in mind that you are only going to get "partial" reset because your cast iron oil boiler must maintain a minimum of around 140 degrees to prevent condensation from occuring in the flues. So, you will be able to reset your boiler temperature from about 140 to 180 or so. this will give you some savings. If you currently have a "stay-hot" boiler, meaning your boiler maintains its internal temperature 24/7, then the tekmar will turn this into a "cold-start" boiler, only running during an actual heat or hot water demand. this increases comfort and fuel savings, especially during the summer months. We honestly have seen around 10 to 15 percent savings with this set-up.
I am using a Tekmar 260 on my Biasi boiler. I'm able to run with full ODR reset (P/S on the heating loops with a TV valve on the return.) I'm also using the optional indoor sensor to allow the 260 to control the system. My oil bills are showing my K factor has increased from the high 6s to over 10; that represents a substantial savings over my old system.