A boiler banging noise can be very disconcerting whether you are a new home owner or have lived in the house for a very long time. A banging noise from the boiler is not necessarily the first sign of a larger problem; however, it is a sign that your boiler system needs some attention. There are many reasons why your boiler or pipes will begin to make noises and the reason(s) why will need to be thoroughly investigated.
The number one reason why you will hear a boiler knocking sound is air build up in the system. Through the process of adding water to the system air will naturally accumulate in your boiler system and pipes. Find the bleeder (or pressure release) valve for your system and slowly let the air escape the system. You will probably hear a hissing noise as the air escapes the system. This should eliminate the banging sound if it is the sole cause of your problem.
Another issue that can lead to banging noises from your boiler is sediment build up in your system. As the sediment settles on the bottom of the tank, when the heating element begins to heat the water, it is blocked by the hard crust of sediment and this will lead to rapid heating of the water, which in turn, creates steam in the system and the banging noises that you are hearing.
Another cause of banging noises from your boiler is a faulty expansion tank or a fast closing zone valve. If either of these parts is not functioning properly they will either need to be repaired or replaced. Replacing or repairing a boiler expansion tank or zone valve is a job best left to a professional. If you believe that this is the cause of your problems, call a service technician to properly diagnose and repair your boiler system.