I have a Raypak R-406a heater, and I'm getting ROL and PRS "Clean filter/strainer" codes. I'm not an HVAC or pool guy, but I have been doing my research. As an aside- last year we had ice damage and I had to replace all valves and the filter, as well as the header gasket in the heater.
It seems for the ROL, it is common for spider webs to cause clogs somewhere. I wouldn't know where on the unit to look for this. I'm also noticing that the unit isn't clicking or firing up at all, but I'm not sure if the PRS error would cause that. As far as pressure goes, the skimmer is clean and I have high pressure (not sure of the exact PSI but it's in the 20s). It has brand spanking new cartridge filters- like installed yesterday.
Here are a few pictures of what I'm working with...