Replacement Motherboad in the UK

I do repairs for a living. I often refuse to repair liquid damaged iPhones if I see extensive damage and feel they are going to fail soon, because the owner of the phone is going to have to pay for the repair that may be only temporary, and possibly for housing parts such as the screen, the front cam cable, the battery, etc.

What I mean to get to is, if they tell you the damage to the iPhone is extensive, don't invest in it anymore.

Otherwise, we usually find logic boards on the likes of eBay. There is a possibility that such boards are not in great condition, or stolen/iCloud locked, and you wouldn't be able to tell until it may be too late. Finally, often a board in good shape, not iCloud locked, and with accompanying home button (the home button has to be the one originally paired with the board if you want to retain Touch ID) should cost you at least 50% of the value of the phone (a good condition phone). Good luck with your shopping.