replace every 2 years. some insurances won't do it until 3 years.
but truthfully, a PARI ProNeb ultra is about $90. So I would pay cash if need be if the protocol was 3 years with insurance.
also, it's important to check the filter. the compressor may be working fine but a dirty filter can cause med times to be incredibly long.
<img src="i/expressions/face-icon-small-smile.gif" border="0"> hope this helps!