Hi, my name is ***** ***** I have been in the home improvement and repair field for 20 years. I will be very glad to help you today. Almost certainly there is a flow issue and the pump is failing or there is a blockage in the piping. When the flow is obstructed or slow the water over heats in the boiler and you get a kettling effect which is the water over heating in the boiler. If the circulation pump is getting really hot then that is a good indication that the pump is failing. Otherwise if the pump is working fine it may take getting the system flushed to remove the blockage.
where exactly is the circulating pump?
The pump itself is on the piping. The exact location would be difficult to assess since it would be anywhere on the piping that the plumber felt was the best location for that particular plumbing system.