I have a gas boiler and sometimes it won't stop circulating in part of the house, and sometimes all of the house. Sometimes it works fine. Any ideas?

More details please... Thermostat could be the problem, sticking aquastat perhaps. Is the boiler pump running or the heat, or both? Any number of things could be causing this issue. Is your house zoned? Saying "part of the house" and "all of the house" leads me to believe it is.