The Horstmann 425 coronet connections are as below.
View attachment 164422
The wire in E goes to the Hive earth tether
The wire in N goes to the Hive N
The wire in L goes to the Hive L
The wire in 4 (timed output 'ON') goes to Hive 3 (Heating On)
Add a wire link to connect the Hive L and Hive 1 (Common) terminals
Depending on the original wiring method used, if there is more than one wire in any of the terminals, all of the wires will need to be moved accordingly.
Finally, because the Hive carries out the functions of a thermostat as well as providing time control, the old wired thermostat needs to be decommissioned to prevent it overriding the Hive. It can't simply be disconnected as this would leave the wiring 'open circuit' and the heating will not operate. The existing room thermostat can be decommissioned in several ways, here are a few. Number 1 is the professional way to do it.
1. Find the origin of the cable that goes to the thermostat. Note where the wires are connected and disconnect the cable. Then add a link between the terminals where the two ‘live’ switching wires have just been removed from so that they are connected together.
2. Remove the existing thermostat and replace it with a junction box, connect the two ‘live’ switching wires together and isolate / insulate the neutral (if there is one)
3. Leave the existing room thermostat in place and join the ‘live’ switching wires together in a separate connector that you can tuck away in the corner of it.
4. Alternatively the original thermostat can simply be set to its maximum setting. However there is always a risk of it getting inadvertently moved, and if it's battery powered the batteries will have to be maintained.