Help wiring nest 3rd generation thermostat

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Hello, Im trying to replace my existing salus stat with a nest 3rd generation stat. The previous owner swapped the standard boiler for a combi, took out the tank and so left with whatever wiring mess hes made. I have a Bosch CDI combi boiler and a Honeywell ST programmer and Salus manual thermostat. The remains of the wiring up in the airing cupboard are just in a choc block. I would like to replace the existing thermostat for the nest and so use the stat wires to connect to the 12V nest heat link connections so it can be in the same place and then the heat link will replace the programmer. (programmer is 1m from the boiler, airing cupboard upstairs and stat in hallway) Im hoping something is possible otherwise I will have to buy the stand and power adapted to plug it in.

I have used a multimeter to continuity check all the wires to map locations (see image) if anything like the previous owners other botch jobs its bound to be strange how its been connected. Ive labelled all the wires for ease and hope someone has experience fitting the same who can let me know what to connect to what to get this to work. I did try a wire diagram but looked a little like spaghetti junction and more confusing. Thanks.
nest install.jpg
 
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CBW

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Essentially what you need to do is the 2 wires at the Salus room stat need to go back to heat link to T1 and T2. Live and neutrals are straightforward, link L to 2 (either LS from boiler, a link wire, or a live common), and 3 goes to LR at boiler.
 
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Unfortunately it’s not that straight forward as need to switch the use of some of the wires, if you see from the plan
 
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