my combi boiler is oil fired and it is running to often and is also short c?

Please help! Our boiler runs to frequently and short cycles, etc.we have a burhnam boiler (r6-110) with a becket burner(al-169356).the boiler has a coil for domestic hot water. There are three taco (571-2) zone valves and a Honeywell control (not sure if label # is the model of it lb124c1102).One zone is always set at 45 degrees it is a vacant in-law apt. The boiler high limit is 170 low is 150 and differential is 10. we have three ritetemp thermostat and all have a swing of 6. Also pressure is 20lb and temp goes up to 220 on bopiler guage. thank you Tom

soreback
January 2011