Hi, my name is Mike and I have been in the home improvement and repair field for 20 years. I will be very glad to help you today. If the noise is seeming to happen as soon as the boiler fires to heat the water then the issue is very likely that the CO2 ratio is needing adjusting. Unfortunately unless you are an engineer it will take a professional to measure and adjust accordingly. This actually is a very common issue with these boilers and a quick adjustment and measuring will get it quiet again.
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