Installing temperature differential switch

Sgancarz

I have a Peerless MI series boiler installed in my house with traditional cast iron radiators.  The house was built in 1910 and is fairly large with minimal insulation.  It still contains all knob and tube wiring so I can't insulate until I have rewired the entire house.  My gas bills are obviously quite high and I was looking for a way to reduce those bills a little until I can rewire and insulate.



I keep the thermostat pretty low (63-65) during occupied hours and set back to 60 at night and when away from the house.  When the boiler kicks on after a setback it will run for quite a while until the thermostat is satisfied.  With that the radiators will get extremely hot. 



I just installed a surface mount temperature differential switch on the return to the boiler (this past week).  I have it set to 120 degrees with a 10 degree fixed differential.  Once the return temp reaches the set temp it will shut down the burner, but the pump will continue to run.  Once the return temp drops 10 degrees the burner kicks back in.  I sat and timed it when first installed and it takes about 20 minutes for the temp to drop the 10 degrees and another 20 minutes to rise back to the set temp.



My question is;

1.  Do you think this will reduce my fuel costs?

2. With this low of a return temp, will I run into problems with condensing of the boiler?