A number of techniques including weight loss coupons and corrosion probes have been used to
study mild steel corrosion in system water typically used in domestic central heating systems. The
corrosion in domestic central heating systems can be controlled by correct system installation and
commissioning, including the addition of an appropriate chemical corrosion inhibitor to the circulation
water. Nevertheless poor practice is common and many systems accumulate significant amounts of
corrosion products in the form of voluminous sludge. This paper reports the results of an independent
study to examine the effect of such system corrosion debris has on boiler energy efficiency and
system effectiveness. By measuring boiler efficiency and analyzing using thermal imaging, the study
shows quantitatively that progressively fouling the system with corrosion deposits serves to
substantially reduce active radiator area whilst decreasing boiler efficiency. Correctly cleaning and
power flushing the system was shown to fully restore the system's hydraulic balance, increasing
fundamental heat transfer capabilities of radiators, increasing overall boiler energy efficiency thereby
minimizing domestic boiler CO2 emission. UK heating systems account for 30% of the country's CO2
emissions and even a modest restoration of boiler efficiency (or prevention of efficiency loss) as a
result of improved practice could have significant impact on this figure.
Key words: Cleaning, Efficiency, Sludge, Cleaner, Inhibitor, Corrosion