When to replace a microwave wave guard cover
It is possible that your wave guard cover can become damaged during normal use. Over time the waveguide cover can absorb, or become splattered with fat or food. This may cause the cover to become soft, overly-flexible or even overheat/burn, causing sparking around the waveguide cover during use. You need to replace the waveguide cover if it has fallen off, has a hole in it, or has any signs of burning or damage. A faulty or damaged wave guard cover can cause your microwave to cook your food unevenly.
The purpose of a microwave wave guard cover
The purpose of a microwave wave Guard cover is to shield the opening through which the microwaves enter the oven cavity. Microwaves are produced by the Magnetron behind the control panel and the wave guard cover prevents food particles and moisture getting into the internal workings of the microwave. During use or cleaning your wave guard cover can become damaged and may need to be replaced.
In the interest of consumer safety wave guards should only be fitted by a suitably qualified person with the machine disconnected from the mains supply.