All enamels and paints for radiators have general requirements: they must protect metal surfaces from corrosion, not yellow or flake off under the influence of high temperatures.
The European "thermal standard" for radiator paints is up to 140-180 degrees. But this is not the limit - there are those that can withstand up to 600. For our central heating systems, paints and varnishes are suitable that normally withstand a surface temperature of 60-80 degrees Celsius. Therefore, for painting radiators and convectors in apartments, ordinary alkyd enamels or familiar oil paints are often used. This option is acceptable, but not always.
What to do if you need to paint pipes in the bathroom, where there is high humidity, and the temperature is "at the limit." The same question is asked if it is necessary to update the appearance of hot water boilers, fireplace grates, etc. In such cases, they usually use either complex systems (which necessarily include an anti-corrosion primer) or special paints and varnishes.
The procedure for applying radiator paints and enamels
If you are going to make repairs in the winter when the central heating system is on, then the first thing you need to make sure is the temperature conditions of the application. Many enamels and paints recommend painting radiators only when the system is off. Without taking this into account, you run the risk of getting a yellowish coating (if you paint with white paint) and not very even and smooth (the paint will dry too quickly and unevenly, without having time to "spread" in an even layer).
The surface must be clean, dry and free from dust or grease. Unpainted radiators should be degreased, lightly sanded and, after removing dust, covered with a layer of anticorrosive primer (manufacturers usually recommend a primer in the operating instructions that works best with this paint).
If the radiator was previously painted, but the paint layer is bad (cracked, peeling, etc.), then it must be removed and then proceed as with an unpainted radiator. If the old layer of paint is strong and you are not satisfied with just its color, then you just need to lightly sand the surface with sandpaper until it is dull and then wash it with some detergent to remove grease stains and dust.
Radiators are painted with a brush (less often with a paint sprayer or roller - this is less convenient) in 1-2 layers. By the way, it is worth taking care of the brush in advance - depending on what kind of radiator you have installed - a brush with a long handle or, conversely, a brush with a long handle, or, conversely, with a small one, thick or thin … If two layers are applied, then after the first layer dries it is necessary to process with sandpaper.