Maintenance is part of what you paid for
The main reason to hire a professional installer instead of hanging lights yourself is what happens in mid-December when a section goes dark. Most professional packages include in-season service calls: the crew that installed your display comes back and fixes it, usually within a few days. Before the season starts, know your installer's service terms — how you report a problem, the typical response time they commit to, and whether service calls are included or billed. If a company won't state its maintenance terms, that tells you something about how January will go.
What you can safely check from the ground
A few observations — all from ground level, none involving a ladder — help your installer diagnose faster. Note exactly which section is out: one strand, one side of the roofline, the wrapped trees, or everything at once. Everything-at-once usually points to power: check whether the outdoor outlet's GFCI has tripped (press reset on the outlet if it's reachable without a ladder) and whether a timer or smart plug lost its schedule after a power blip. Partial outages usually mean a failed strand or connection up high — that's the installer's job, not yours. Take a phone photo of the dark section at night; it's the single most useful thing you can send with a service request.
What not to attempt — and why installers insist on this
Do not go up a ladder to fix holiday lights in winter. This is not boilerplate caution: December ladder work means cold-stiffened cables, gloved hands, ice you can't see from below, and frozen gutters that clips are anchored to. Don't unplug and reseat connections on the roofline, don't swap bulbs in an energized strand, and don't handle any connection that's wet or iced. Professional crews carry the right footwear, anchoring, and replacement material, and your agreement almost certainly makes roof-level work their responsibility — doing it yourself can also void the maintenance terms you already paid for. The complete list of what a homeowner should do above ground level is: nothing.
Timers, controllers, and the failures that aren't failures
A surprising share of 'my lights are broken' calls are schedules, not strands. If the display simply isn't turning on at the usual time, check the obvious first: a mechanical timer that lost its dial position after an outage, a smart plug that dropped off Wi-Fi, or a photocell now shaded by something new. If your installer set up the timer, ask them to walk you through it at install time — thirty seconds of explanation prevents most of these calls. When the display misbehaves in stranger ways (sections flickering, colors wrong on an RGB system), report it rather than experimenting; controller issues are diagnostic work, and cycling power repeatedly can make the fault harder to find.