Hot H2O heating system problem

Sadowski

Recently bought 72 year old house with hot water heating system (40-50+) yrs. old. The system consists of cast iron boiler, appropriate piping, a circulating pump with heat exchangers in each room. Some exchangers are of the expanded copper tube type and are located in the walls near the floor, with flues near the ceiling and conventional radiators mainly under windows which are enclosed within the walls. Over the past couple of weeks we have noticed intermittant activity of the raditiors. Different raditiors work on-off in different rooms at different times? Pressure in boiler runs 5-7 adding h20 increases pressure easily but drops to 5-7 within 10 minutes. Circulating pumps seems to be running.Have had two heating guys out who seem stumped. No leaks found. One pipe to garage is underground and can't inspect but this raditior seems the hotest in the house and is closest to boiler. Can you have low pressure without leak? If it was leaking, shouldn't we notice it somewhere?
First and second floor are poured concrete, house sits on 2.5 ft. crawl space. Any ideas? Need heat in Northwest Ohio.

Sadowski

Sadowski