Fair enough. I may have been wrong legally. I respect your opinion and realize you are logical, unbiased, and knowledgeable. Your view/advice may be different than mine.
This is my view/advice
When you take into account the reduced refund to take account for the 4 years of use you would probably be left with 20 percent of the original cost. When you take into account that almost every TV with burn in issues is going to be a 4 year or older television it may not be practical to file a claim. The outcome, in favor of the claimant, may be different for a 4 year old TV than a 18 month old TV.
It would probably be better to go directly to LG and request a 20 percent refund. The chances of you getting compensated this way is far more likely than taking LG or the retailer to court in my opinion.
Thank you for your reasonable response, too often people are obstinate online when they get something wrong. I include myself in that, it's just human nature.
Just to be clear the following is based on UK Law and consumer rights, other jurisdictions would be different.
I think you're basing your calculations of any reduction on depreciation. That is not the case here. As DBWinter highlighted, what matters here is how long one could reasonably expect the product to last.
The CRA doesn't specify these expectations explicitly, it's often left to the judges interpretation (fo previous cases, contemporary expectations) and judgement. But I very much doubt anyone would argue its reasonable for a TV to fail in 5 years, therefore it's very unlikely you'd only get 20% back.
The principle in UK law is that one should be returned to their original position, not gain or lose due to a breach. So for arguments sake lets say the judge deems a premium TV should last for 12 years and it has failed after 4 years, he may deduct 1/3rd for the usage you've already had.
Of course its not as clear cut as "it failed after 4 years so its not fit for purpose". The CRA isn't meant to be an iron clad guarantee, more protection against products that are not fit for purpose. In the first 6 months, the burden falls entirely on the retailer to establish any fault was not inherent. After that the burden shifts to the consumer. So the consumer may well be expected to get a professional report if the fault is obscure and its hard to prove the fault was inherent with the product.
In the case of burn in, I think LG's disclaimers actually help the consumer. They have essentially acknowledged openly there is a potential issue with these TV's. But said it should not present with normal usage. So if you suffer burn in through normal usage, then you have a good argument there. How do you prove normal usage, well the type of burn in your panel has would probably help.
If you have a windows desktop burnt into your panel, you're probably going to have a hard time arguing you used the TV normally. Also if you have a large part of a frame burnt in, you may have difficulty as that would suggest you may have left the image on pause/etc. If on the other hand its a DOG, well they are ubiquitous so how could LG argue your watching channels with DOG's was not normal usage. Same applies for other partial parts of frames burnt in. Football score, etc, etc.
NB: I'm not a lawyer, but this is my practical experience of having used this legislation against retailers over the years.
It's also important to remember in the UK your contract is with the retailer not the manufacturer. So it would be the retailer you take to court. And if you buy using a credit card, then the CCA makes the card company jointly and severally liable. Which means you can also take them to court. But before that you can try a Section 75 claim agains the card provider, which may be easier.
I've tried to keep this as succinct as possible, as this isn't a general legal advice forum or thread. Anyone in a similar position to the OP would do well to speak to Citizens Advice, check if they have legal advice covered in their Home insurance/etc, or read the act itself and some similar cases.
NB: One more important point is any claim would go to small claims court. These courts are there to cater for smaller claims and more friendly to the lay. So I appreciate in general one should be very careful considering legal action as costs can spiral. This is not usually the case in small claims court. Nor do you have to be Perry Mason to avail of their services. In fact, quite often big companies don't show up. As many of them unfortunately operate their CS as a war of attrition. They don't care if you're right or wrong, they just make you jump through hoops in the hope most will give up.
If you're interested there's plenty online about the CRA, small claims courts and fit for purpose.