There is a quick way to get "warranty issues" resolved.
Firstly, there is mandatory warranty that states a product must be warranted for a length of time that a reasonable person would expect said product to last for.
I have succesfully used this a few times against HP. They give you a 12 month warranty, but the service life of a PC is given as 3 years, hence, a reasonable person can expect it to last 3 years.
Call up, with the phone call being recorded (As an individual you are legally allowed to do this without telling PWR, if you're a business, it's a no no), and ask them how long they normally expect their radiators to last. Do NOT tell them who you are etc etc at the beginning of the call, make it sound like you're interested in the products etc.
Once you have a valid length of time, you just gotta be like "well you sound like a reasonable bloke, and if you expect it to last 4 years, well, I've got this one that is only 18 months old, you can cover it via warranty"