Start with the words that come before the coverage list. Many service contracts and warranties have a section that sets the condition of the system at the start. It may be called pre-existing condition, prior condition, known condition, or something close. The line tells you what the contract assumes was already true when you signed. Read it before the coverage list, because it can narrow what the list means.
What the clause usually does
In general terms, a pre-existing condition clause excludes a fault that was present, or was known to the seller or the contract company, before coverage began. The clause often points back to a fixed moment, such as the sale, the signing, or the last inspection. Some contracts exclude only faults you knew about. Others exclude anything an inspection would have shown. The wording decides which one you have.
Pay attention to the trigger words. Known and discovered describe what someone was aware of. Existing and present describe what was physically there. A fault can exist without anyone knowing about it. Ask which standard the contract uses.
Walk the paper
Check these items in the contract itself, not in the sales summary.
Find the look-back point. Is it the date you sign, the date coverage starts, or the date of the last service? Copy that point into your own file.
Find whether the clause requires a pre-coverage inspection. Some contracts ask for an inspection report or a check of the system before coverage begins. If a report is required, find out who writes it, who receives it, and what happens if it is missing.
Find what the contract says about the age and condition of the system at signing. Some contracts set an age limit or a condition requirement. A system outside the stated range may be excluded or may need a separate review.
Find whether a repair made before coverage starts counts as a cure. A prior repair does not always clear the record. Check whether the contract wants that repair documented.
Find the burden of proof. Some contracts leave the job of showing a fault is new with the person making the claim. Others leave it with the company. Know which side carries it before a claim is ever opened.
Questions to ask before you sign
Ask the seller or the contract company these questions, and get the answers in writing.
What is the look-back point, and is it written in the contract or only in a sales summary?
Is a pre-coverage inspection required? If so, who performs it, and is there a charge for it?
What record do you keep of a fault I report at signing, and can I get a copy of it?
Does a repair I made before coverage started count against a later claim?
What proof do you need to show that a fault began after coverage started?
Compare the record against the system
Keep your own file. Write down the install year of each system, any repair you know about, and any unusual behavior you noticed before signing. The walk-through pages and system guides on this site are built for that kind of log. For a furnace, the gas furnace guide turns an install year into a planning date. For a heat pump, the heat pump guide does the same. The published figures live in those pages, so this piece does not repeat them.
If the record shows a fault before signing, write it down and keep the note with the contract. A short note made the day you saw the fault is worth more than a memory you rebuild later.
What this clause does not decide
The clause sets a starting point. It does not tell you whether any particular claim will be paid. Coverage depends on the full contract, the terms that apply to your system, and the facts of the fault. Read the exclusions and the claim steps together with this clause. Where the wording is unclear, ask for the answer in writing before you need it.