Start with the paper, not the phone call. A service contract is a set of written terms, and those terms decide when coverage begins and what counts as a problem that was already there. Read those lines before you compare anything else.
What a waiting period is
A waiting period is the gap between the day you sign and the day coverage can be used. Some contracts apply one. Others start coverage at signing. The contract should state the length of the gap and what starts the clock: signing, payment, or a later activation step. Write that start point on your own file the day you sign.
What a pre-existing condition line does
Many contracts exclude a failure that was already developing when coverage started. The provider may ask you to confirm the system works. Some ask for an inspection. Others rely on your statement. Read the wording closely. Find out who decides whether a condition was present at the start, what evidence is accepted, and whether you can add a photo, a service note, or a written statement from the technician who last serviced the unit.
Walk the terms before you sign
Check these lines in order. Find the start rule and the waiting period. Find the pre-existing condition wording and the evidence it accepts. Find what is covered for the specific system you own, not only the general list. Find the cancellation rule and how any refund is figured, including whether it is based on time used. Find the transfer rule in case you sell the home. Find the renewal rule and the notice you get before a charge changes.
Questions to put in writing
Ask the provider these before you sign, and ask for the answers in writing. When does coverage start, and does a waiting period apply to this system? What do you need from me to show the system was working at the start? If a fault appears inside the waiting period, what happens? Who decides whether a failure was already present? If I sell the home, does the contract transfer, and what does the transfer require? If I cancel early, how is the refund calculated?
Keep your side of the record
Your file is your side of the contract. Keep the install year, the model, the last service visit, and the date you signed. Photograph the unit and its data label. Keep copies of every email and a written summary of every call. If a question comes up later, that file is the evidence you bring to it.
Where the figures live
This page covers the terms, not the numbers. Each system has its own typical service life and planning window. For a furnace, read the gas furnace page. For cooling, read the central air conditioner page. Use those planning windows to decide whether a contract is worth reading in full, and use the terms above to decide whether it is worth signing.