A boiler is the main source of water heating in most homes. Like any other device, it can go haywire and come under the need for repairs. Gurgling noises in a boiler are a fairly common problem. Below are two possible causes.
High Thermostat Setting
The thermostat regulates the temperature at which water is heated. If set too high, this heat can cause bubbling as the water heats up. Once the hot water has been circulated, the gurgle will disappear. Adjust temperature on the controls and to a lower setting and the sound should cease.
A pocket of air may form somewhere in the heating system, which can also cause gurgling noises. If this is the cause, you'll need to bleed the radiator to eliminate the air lock. You can pick up a small radiator key from a hardware shop. Be sure to prepare a small basin and some rags to capture the water you release.
Insert the key into the slot at the top of the radiator, then turn on the heating. Slowly turn the key to release water and air through the valve. As air is released, you'll hear the radiator gurgle. This will disappear once all the air has been released. You can then tighten the valve.