When the heat is turned on, water is heard rushing through the pipes. The boiler is gas fired.

When the heat is turned on, water is heard rushing through the pipes. The boiler is gas fired.
If the system has been dormant for an extended period, air may have moved to the higher points in the loop. After the heat has been run for a while, these symptoms should dissipate.
If they don't you will need to have excess air purged.