Hi, central heating can run between 60 and 90 degrees Centigrade, 82C is the standard so is pretty hot anyway. This is normally controlled by the boiler thermostat but if this fails then there should be a limit stat that should cutout the boiler if the temperature reaches 100 - 120 degrees. You could try turning down the boiler thermostat to see if that has any effect.
The other cause is related to my previous answer where if the water level is low in the system then this could also cause the temperature to raise to boiling, but should cutout on the thermostats. Both problems are linked and could be making the system noisey.
If hubby hasn't the time to check this get someone in quickly as boiling water in the system can be very dangerous, it can also cause the plastic tank to melt in the loft causing a flood! Don't use it if you think it is boiling.