Boiler makes banging noise when firing up

A loud banging noise coming out of a boiler is surely a matter of concern. Anyone in that case would wonder as to why the boiler makes banging noise when firing up. Well, there can be two reasons to this-

1. If your boiler makes a single BANG only when it fires up, it’s most likely due to delayed ignition- The problem of delayed ignition is quite commonly found in gas boilers that use pilot lights in contrast to the electronic ignition systems. When a gas boiler receives the call for heat, the gas valve opens and releases a small amount of gas into a sealed combustion chamber through small “jets”. This gas then gets ignited by the pilot light and the jet flames heat up the heat exchanger. Delayed ignition occurs when the gas that is sent into the combustion chamber doesn’t immediately ignite. And when that happens, the gas builds and builds inside the combustion chamber until bang, creating a mini explosion.
2. Problems causing Delayed Ignition
3. Not enough gas
4. Not enough surrounding air
5. Dirty burners
6. A bad gas pilot light
7. What can we do about it?

In case of a delayed ignition, we would highly recommend you to fall for the professional help, as the intensity of the flames caused by the gas buildup can eventually cause your boiler’s heat exchanger to crack, which might let out the carbon monoxide gas off the combustion chamber, resulting into carbon monoxide poisoning which can be very harmful.

1. If your boiler makes recurring banging, popping noises as it operates, it’s most likely due to “kettling”- Kettling is something which occurs as a result of the lime scale buildup in the system that eventually creates bubbles and leads to the occurrence of ‘hot spots’.  These hot spots are what causes loud noise and needs to be treated with a solution in order to clear the lime scale blockage. However there are a number of other reasons as well that can cause kettling.
2. Problems that cause kettling
3. Lime scale deposits on the heat exchanger
4. Water pressure/flow is too low- When the water flow is too low, water runs over the heat exchanger much slower than it should. This slower pace causes the water to overheat, thus giving rise to steam bubbles which erupt forcefully when they reach cooler water.
5. Bad thermostat-If you have a faulty boiler thermostat, it would allow the burners to stay on longer than it should thus causing the heat exchanger to overheat. Therefore, when water comes into contact with the extremely hot heat exchanger, steam bubbles are created, which then erupt noisily.
6. Water temperature on boiler is set too high- Setting your boiler to a very high temperature can overheat the water, causing steam bubbles and eventually resulting into a banging noise.
7. What can we do about it?

In this case you could either bleed your system or repressurise it. However, we would recommend you to consult a professional help regarding the same in order to avoid any danger to self.