Boiler will go to set temp //shut off then not cycle back on when temp drops below setting.. if I turn the thermstat off then back on it will heat to set temp but not come back on.. pump doesn't seem to shut off even at 5-6 degrees below set temp.theromstat is a RobertShaw on a wellsMclain boiler.. thanks

I don't quite understand about the pump. The thermostat usually has a red wire to an R terminal, and a white wire to a W terminal. Shut the power off to the system and remove the thermostat from the wall. Remove the red and white wires and connect them. Turn the power back on. The boiler should come on normally. Let it heat for a while and then disconnect the wires. The boiler should go through its normal shutdown cycle. After the house cools a bit, connect the wires again. If the boiler starts up normally, the problem is in the thermostat. All it does is switch power from the red wire to the white.

If the pump runs when the boiler isn't firing, that is a different problem, most likely a stuck relay.

labman is probably right about this one sounds like what u are saying is that the circulator doesn't shut off boilers are set up 1 of 2 ways either on a cold start system... this is where the boiler only runs when there is a call for heat or hot water... or on a maintaining which is where the boiler will maintain a set temperature based on the settings on the control normally 160-180 degrees if your system does not restart itself without resetting the tstat more than likely the aquastat relay is sticking and by lowering and raising the t-stat you're in essence resetting the relay usually u can get these at a local supply house
But they can be pretty costly usually a cold start control will run u about 100 dollars where as a maintaining control will be in the 150 range