With winter coming up, I started to heat the house and for the first time the radiator pipes are starting to whistle when I heat and then shut down the system. I have a big house and I need to shut down the heating system regularly if I do not want to blow out my budget. I went in the basement to inspect the system and I saw that the bottom of my boiler is leaking: could this be the reason why the pipes are whistling or is the issue coming from an another source?
You might have air in the pipework to the radiators. You can bleed air from the system's heating circuit (usually a bleed valve is present at the highest point in the pipework)
and from individual radiators.
Details vary depending on which side of the planet you are standing.