What do we mean by Kettling in Boilers ?

Kettling refers to the sound of boiling water coming from the boiler.  It is similar to the sound coming from a tea kettle.  Hence, the name. 
Kettling noises can have a number of causes.  Some of them are


Deposits
If the water quality is not properly maintained, deposits can form on the bottom of the boiler.  This is particularly in areas where the water is hard, resulting in limescale deposits.  The deposits prevent proper heat transfer between the water and boiler.  This uneven heating can cause kettling.

Flow rate
If the flow rate of the water is not proper, the water can get overheated as the "dwell time" will be more. this can result in kettling.  The flow rate of the boiler should be reviewed. 

Improper Thermostat Settings
If the thermostat settings are not proper, they may result in overheating. 

Improper Burner functioning
If the burner of the boiler is not properly function, kettling can result to uneven heating. 

Improper Installation
Improper installation can also cause kettling.  If the noise occurs soon after installation, do contact the manufacturer.

Kettling Noises should always be investigated as they affect efficiency and may point to other problems