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Thanks OG for that link, as it uncovered the major problem that was an ice blockage.
I found a video on YouTube, with the exact same fridge and the exact same problem, and have spent the past couple of hours with all the food out on the table and a hairdryer in my hand, melting an ice block that would sink the Titanic!
The hardest part was getting the back panel off the bloody fridge, as it was literally stuck in place with ice.
Put it all back together and plugged in the fridge in. Temperature came up as 23 degrees!!! Major sad face :-(
Sat and waited, and it's just this minute hit 3 degrees. I can also hear the fan going round, and it's not making a 'struggling' noise.
Thanks so much for that link, I would never have thought of ice, but seems it's a common fault.