fur up
phrasal verbPart offur
fur up — phrasal verb
1. to become covered on the inside with a hard layer of mineral deposits (limescale
1.phrasal verb
Definition
to become covered on the inside with a hard layer of mineral deposits (limescale), especially in a kettle, pipe, or water heater.
Example
This kettle has furred up badly because we never descale it.
The hot water pipes in the old house had furred up over decades of use.