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Boiler noise, or ‘kettling’, has a number of potential causes, and these can be divided into chemical and mechanical factors.
Foaming system water reduces the contact between water and the heat exchanger, leading to overheating. The foam which is responsible for this overheating can be produced by number of things, such as excessive residual flux, suspended solids, or other contaminants.
Washing up liquid is falsely reputed to minimise boiler noise, and some individuals have in the past introduced it into central heating systems, unaware that this actually generates foaming, one of the principal causes of boiler noise. It also introduces high levels of corrosive chloride.
Deposits are excellent insulators and partial insulation of the heat exchanger surface can cause uneven heating and the associated boiler noise. In central heating systems, such deposits will likely be corrosion debris or thin limescale deposits.
In hard water areas, limescale forms in the hottest part of the system – the heat exchanger surface – generating thin and patchy deposits of scale which increases over-design heat transfer temperatures at other parts of the heat exchanger surface. This leads to kettling.
When a maladjusted highl-rated boiler is fitted to a small system, the boiler will cycle rapidly, with the heat exchanger unable to dissipate the heat. This results in localised boiling, increasing boiler noise.
An incorrect flow rate can restrict the heat dissipation in the boiler, leading to local boiling and therefore kettling.
If the boiler thermostat is not operating correctly, it should be replaced to ensure overheating does not occur.
If thermostatic radiator valves are fitted on every radiator, they can cause a boiler to cycle rapidly and overheat.
If the cold feed and open vent pipes have been incorrectly sized and fitted, system imbalance can result.
In cast iron heat exchangers, faults in the casting can promote non-uniform heat transfer and as a result, localised overheating.
First eliminate the mechanical factors mentioned above as the causes of boiler noise. If you have done so, the assumption can be made that deposits on the heat exchanger are to blame for the kettling issue.
You can either treat the system with a leave-in product such as Sentinel X200 Noise Reducer which will soften and gently remove this scale, or, for a more long-term solution and if you suspect that other areas of the system are affected, the system should be cleaned using the most appropriate chemical from the Sentinel range of cleaners.
