They could potentially claim that the screens blocked air intake for combustion air supply.
If the screens were too restrictive, they could reduce air supply below the required air intake for complete combustion.
The newer model has fewer air vents, so screens with poor airflow could cause the heater to malfunction.
Properly sized screen mesh should be small enough to keep out mice, but not so small as to obstruct airflow.
Most likely, the screens sold by MK are probably OK.

If the screens were too restrictive, they could reduce air supply below the required air intake for complete combustion.
The newer model has fewer air vents, so screens with poor airflow could cause the heater to malfunction.
Properly sized screen mesh should be small enough to keep out mice, but not so small as to obstruct airflow.
Most likely, the screens sold by MK are probably OK.
