Most boilers come with a manufacturer’s warranty. But after a few years, we experience some common boiler problems. Such problems can be addressed without the need to call a heating engineer; others will require the services of a qualified and experienced professional.
1. (a) priming (b) foaming (c) carry over
2. Boiler corrosion
3. Scale sludge and formation
4. Caustic embitterment
1. Priming Foaming and Carry Over: when steam is produced rapidly in the boiler some small droplets of the liquid water are carried along with the steam. The steam with some small water droplets is called “wet steam “.
(a) Priming: The process of formation of wet steam is called priming. Priming also starts when level of water rises due to foaming. So priming is generally associated with foaming.
(b) Foaming: The formation of foam or bubbles at the water surface in boilers is called foaming which does not break easily.
(c) Carry over: The phenomenon of carrying of water along with impurities by steam is called “carry over”. This is mainly due to priming and foaming. Priming and foaming mainly occur together.
2. Boiler corrosion: The “decay” or “disintegration” of boiler material either by a chemical or electrochemical reaction with its environment is known as “Boiler corrosion“.
3. Sludge and scale formation: Boilers are used for steam formation. When hard water is continuously evaporated in boilers, the continuous evaporation of water increases the concentration of dissolved salts until the water becomes saturated. Then the salts of Ca++ and Mg++ along with other soluble impurities are precipitated on the inner walls of boilers. When the precipitate formed is soft, slimy and loose, known as sludge and is hard and firmly adhering on the inner walls of boilers, known as scale.
4. Caustic embrittlement: This is the phenomenon during which the boiler material becomes brittle due to the accumulation of caustic substances. It is form of corrosion caused by high concentration of sodium hydroxide in boiler water. It is most likely to occur in boilers operating at high pressures, where NaOH is produced in the boiler by the hydrolysis of some residual Na2CO3 obtained from water softening process like lime soda.
Na2CO3 + H2O = 2NaOH + CO2
The formation of NaOH makes the boiler water caustic. This caustic water penetrates into the minute hair cracks present in the inner side of boiler by capillary action. When the water evaporates and the concentration of dissolved NaOH increases progressively which attracts the surrounding area, thereby dissolving the iron of boiler as sodium ferrate.
Fe + 2NaOH = Na2FeO2 + H2O
Original source - Boilers
The comments appear to be directed more at commercial steam systems, but there is no question that water quality is starting to become a major issue with hydronic systems as well. Here in Vermont, and New England, the use of boilers and hydronic heating is much more common than the rest of the nation, and the water quality of private water sources (drilled wells and springs) varies very widely. Many heating contractors are not paying attention to water quality and with the advent of IFCs (internal flow checks) and the more complex condensing boilers, homeowners are starting to pay the price.
I recently had two calls for no heat just days apart. One was a mid-efficiency low mass boiler, about 10 years old, and the other was a high efficiency condensing boiler, which last year replaced a similar mid-efficiency low mass boiler. Both systems are propane-fired and both have a mixture of radiant and baseboard heating. In both cases, the IFC in a circulator for a radiant zone had become so clogged with rust that there was no flow at all. In the first case, the pressure indicator on the tridicator was completely blocked and the mixing valves had corroded to the point of no longer operating.
It is imperative that heating contractors pay attention to the water quality of water going into their boilers, including makeup feed water, and that they periodically test the boiler water and condition it as needed.