Fan bearings can be noisy on boilers, especially if starting to run dry, so
yours may need greased before they burn and crumble. Also, if the boiler
has the pump built - in, it too can be the culprit of high pitched whining
Check that the system is properly filled to the recommended pressure and
that no bleeding is needed. Water looses volume after having the oxygen
boiled out from it, and the drop in volume may mean the pump is running in
some air, so causing the sounds you hear.
Good luck with it.
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