Verdict: It depends. Manufacturer troubleshooting pages don't describe a gradual, built-in loss of power; they point first to power level, cycle selection, the food itself and household voltage, and a microwave that has truly weakened has a part that needs testing.
Where the idea comes from
A microwave that once heated a mug of coffee in a minute now seems to need a minute and a half. Because the change creeps in slowly, it feels like aging, the same way a car battery fades. Many people also remember the wattage printed on the door and assume it drops over the years.
What the evidence says
Whirlpool's page on microwave cooking times that are too long lists the causes it wants owners to check:
- •Amount: "The more food heated, the longer the cook time needed."
- •Power level: make sure it's set to 100% or the level you want.
- •Cycle: confirm the correct function is selected.
- •Size, shape and starting temperature: smaller pieces heat faster, and refrigerated or frozen food takes longer than room-temperature food.
- •Density and composition: dense foods like meat and potatoes take longer than light, porous ones.
- •Voltage: have a qualified electrician check the home's electrical system.
None of those is age. For a microwave that may not be heating at all, Whirlpool's built-in microwave heating check is simple: put one cup (250 mL) of water on the turntable and run it for one minute on HI (100% power). If the water warms, the microwave is heating.
That doesn't mean a microwave can never weaken. If the settings and food are ruled out and heating is clearly slower than before, the cause sits in the high-voltage parts behind the cabinet, which only a technician should test.
What to do instead
- Check the power level. A level left below 100% from an earlier use will slow heating.
- Compare like with like: the same mug, the same amount of water, starting from cold tap water.
- Run Whirlpool's one-cup, one-minute test on full power and note how warm the water gets.
- Repeat it on a different day. A consistent, clearly weaker result is worth reporting.
- If lights dim or other appliances slow at the same time, ask an electrician to check the voltage.
Exceptions worth knowing
- •Inverter and sensor models adjust power on their own during sensor cycles, so a sensor program isn't a fair speed test.
- •A microwave that hums but doesn't heat, sparks or smells of burning should be unplugged and checked.
- •Never open the outer cabinet. Microwaves contain high-voltage parts that can hold a charge after unplugging.
- •Installation matters too. A countertop model boxed into a cabinet can overheat. See whether a countertop microwave can go inside a cabinet.
Sources
- •Whirlpool: Microwave Cooking Times are Too Long, Countertop Microwave (food, settings and voltage causes)
- •Whirlpool: Not Heating, Built-In Microwave (one-cup, one-minute water test)
The short version: Rule out settings, food and voltage before blaming age, and let a technician test a microwave that's truly weaker.
Water barely warm after the one-minute test? Leave the cabinet closed and call TrueFix Los Angeles at (213) 787-3989, or book microwave repair.