As for CP 12's, it blo0dy easy to see when its an illegal installation. Issuing CP12's on these is again down to pure greed, where a self respecting Rgi would laugh and walk away. Tough shi*e on the dodgy landlords.
And if landlord get a clown to issue CP12's then landlord and Rgi should be reported !!!
I agree with you in the theory, however until CORGI or whoever make it illegal to do a CP12 when the boiler has not been installed by an RGI the landlords will continue to have their boilers installed cheaply and just get a CP12. Nobody polices non RGI fitted boilers. Building Control should but dont make any money out of it so dont.
I asked ARGI a couple of years ago if they would formulate a policy on reporting illegal installs but no one else was interested and some stated they feared reprisals if they did that.
Tony