Repair the siding when the damage is limited to panels and the wood behind them is sound. Replace it when rot has spread through the sheathing, when more than about a third of a wall is affected, or when the profile is no longer made and patches would never match. The only way to know is to open one damaged section and look behind it.
Start by pressing on it
Press firmly on the boards low on the wall, near the ground and under the windows. Sound siding pushes back. If it gives, feels spongy, or a screwdriver sinks into it with hand pressure, the water got past the surface a while ago.
Do the same at the corners and where the siding meets trim. Those joints open up first, and they are where most leaks in older Berkshire homes start.
What tells you a repair will hold
Damage that stays in the panels themselves is usually a repair. A branch cracked three boards in a storm, a section buckled from heat, one run pulled loose. If the wall behind is dry and firm, replacing those pieces is honest work that lasts.
The same goes for gaps and failed caulk. Those are cheap to fix and expensive to ignore.
What tells you it has to come off
Rot in the sheathing behind the siding changes the answer. Once the panel underneath is soft, new siding over it just hides the problem for a season, and it comes back worse and bigger.
Scale matters too. When more than roughly a third of a wall is damaged, patching costs approach replacing, and you end up with a wall that looks patched.
And sometimes the profile is simply discontinued. If nothing on the market matches, every repair reads as a repair from the street.
Why winter changes the plan here
Vinyl gets brittle in deep cold. Cutting and nailing it below freezing risks cracking panels that were fine. Some siding work is better held until spring, and a contractor who tells you that is saving you a callback, not turning down work.
Emergency repairs after a storm are different. Those get done when they happen, because an open wall in January is a much bigger problem.