A service contract and a warranty are both written promises with terms. The promise is only as clear as the words that define it. Read the terms before you sign, and before you rely on them.
What the document is
A warranty usually comes from the maker and covers defects for a stated period. A service contract is usually sold separately and covers repair or replacement under stated conditions. Both are written in similar ways. Look for the parts that say what is covered, what is excluded, what you must do to keep the coverage, and how a claim is made.
Read these parts
Find the term and the start date. Check whether the term begins at purchase, at delivery, or at installation. Find the waiting period, if there is one. A waiting period is the stretch after the contract begins during which claims are not yet accepted. A claim made in that stretch may be refused even if the system has a fault. Note exactly when it ends.
Read the exclusions list in full. Note any condition that depends on maintenance, on the installer, or on who performs the work. Note the claim steps and any response time the document states. Check whether a provider network is named, and whether you may choose your own provider.
Cancellation and transfer
Cancellation rules set out who may cancel, how notice is given, and how any refund is worked out. Read the method and the timing, and keep a copy of the notice you send. Transfer rules say whether the contract moves with the home when it is sold, what the new owner must do, and whether a transfer fee applies. Ask the seller to state each rule in writing.
Questions to ask before you sign
Ask what the waiting period covers and when it ends. Ask what happens to a claim made during it. Ask for the exclusions in writing. Ask how cancellation works, and how transfer works if you sell. Ask who performs the repair and whether the provider is the same company that sold the contract.
For the published figures on typical service life, start with the appliances ranked by typical service life page on this site. Use those figures to judge whether a contract term matches the life you expect from the system, and read the contract's own terms for everything else.
This is general reading guidance and not legal advice. A contract you are unsure about is worth a conversation with a qualified adviser before you sign.