A covered replacement can go wrong after the old unit comes out and before the new one is switched on. The step that often gets missed is the paperwork: a permit that a local office may require, and an inspection that confirms the work met the code in force where you live. Who handles that step is a question to settle before the crew arrives.
Permits and inspections, briefly
A permit is official permission from a local building or code office for certain kinds of work. An inspection is that office's check of the work after it is done. Gas connections, electrical work, water supply, venting and drain connections are common triggers, though the rules vary by place. A permit often has its own fee and its own timeline, and an inspection can fail if the installation does not match the code.
What a contract may and may not settle
A service contract is written to cover the repair or replacement of an item that breaks down. It does not replace the local rules on how that work must be done. Read the contract for any language on permits, code upgrades, and whether the provider's technician or a licensed trade performs the work. Ask whether a permit fee is part of the service, whether an upgrade required by newer code is part of the service, and what happens if an inspection fails after the replacement is in place.
A short sequence to follow
Ask your local building or code office whether a permit is needed for the specific replacement you have in mind. Ask the provider, before the visit, who pulls the permit and who attends the inspection. Get the permit number in writing. Keep the inspection result with your contract file. If an inspection finds a problem, ask in writing who corrects it and under which part of the contract that work falls.
Where to compare the terms
The comparison page on this site lines up the same contract terms for several providers, term by term. Use it to see which providers describe permits or code work at all, then read the actual contract before you rely on that description. This is general information about how these rules usually work, not advice about any particular installation.