Reliability
Condensing boilers are claimed to have a reputation for being less reliable, requiring professional installation and regular service, and may also suffer if worked on by installers and plumbers who may not understand their operation. Claims of unreliability have been contradicted by research carried out by the UK-based Building Research Establishment (see "Myths" below.)
Heat exchangers in condensing boilers are primarily manufactured using stainless steel and aluminum. Initial testing and annual monitoring of the heat transfer fluid in condensing boilers with aluminum or stainless steel heat exchangers is highly recommended. Maintenance of a slightly alkaline (pH 8 to 9) liquid with anti-corrosion and buffering agents reduces corrosion of the aluminum heat exchanger. There is a feeling among some professionals in the field that the condensate produced on the combustion side of the heat exchanger may corrode an aluminum heat exchanger and shorten the boiler's life. Statistical evidence is not yet available since condensing boilers with aluminum heat exchangers have not been in use long enough.
To ensure reliability, condensing boilers must be properly installed and maintained.
Read more about this topic: Condensing Boiler