Service agreements in general tend to draw a line between a breakdown and wear. A failed part is usually a repair question. Worn parts, along with the routine replacements that keep equipment running, often fall to the homeowner. Knowing where that line sits in your own contract keeps a visit from becoming a disagreement about whether a filter should have been changed.
What counts as a wear item
Wear items are parts that are used up on a schedule, whether or not anything has broken. Common examples in a house are air filters, smoke and carbon monoxide detector batteries, water filter cartridges, drain screens and strainers, dryer vent lint buildup, and the door gaskets on a refrigerator or washer. Some appliances have their own consumables, such as ice maker water lines or burner caps on a range. The list changes by appliance, so the most useful starting point is the owner's manual for each unit.
Read the contract's own line
Look for language that separates a breakdown from routine maintenance or normal wear. Agreements often say the homeowner must keep equipment in working order and perform the upkeep the manufacturer requires. Some spell that upkeep out. Others only refer to it. Find the clause, note what it asks of you, and write down the schedule it implies. If the contract is silent, ask the provider in writing what it expects before a visit depends on the answer.
Keep a simple upkeep log
A short log that records when each wear item was changed, which part you used, and where you bought it gives you a record if a technician asks. It does not need a spreadsheet. A notebook or a note on your phone is enough. Keep receipts for parts you buy, since they are the evidence that a routine job was done.
When the line is unclear
If a visit turns on whether a worn part caused the failure, ask the technician to note what they found and why, and ask for that reason in writing. If you did the work yourself, say so when you describe it, and keep any part you removed until the visit closes in case the technician wants to see it. Where the contract is unclear, a short written question sent before the visit works better than a disagreement at the door. If you are still choosing an agreement, the sample contract page lists agreements you can read before you buy.