Nest gen 3 to replace Honeywell ST9400C double check wiring

[mentalmike]

Replacing a Honeywell ST9400C timer with a nest gen 3 for a friend and just wanted a second opinion I've got this correct.

He's got a y layout system with this loverly nest of wires in wiring centre

Honeywell ST9400 wiring - only has N L 1 3 4 connected

So it follows Y plan wiring except for:

• A red wire going from 5 to the boiler which is unused
• Pump goes to 9 rather than 8
• Boiler live goes to 1 rather than 8
• An extra wire goes to 9 from boiler

So this is what I think I need to do

• 1 to nest L, 2 and 5
• 2 to nest N
• 4 to nest 3 (Old timer 4 to nest 3)
• 7 to nest 4 (Old timer 1 to nest 4)
• 6 to nest 6 (Old timer 3 to nest 6)
• Remove old stat wires connected to 2, 4 and 5
• Connect 4 and 5 ?? in pink

Originally the extra connections in 9 threw me but after locating an additional block of connectors by the boiler (Worcester bosch greenstar 18ri) and looking at it's wiring diagram I guess explains terminal 9... the boiler is clearly a replacement for an older one where it wouldn't have had this feature and seeing as the boiler is located no where near the pump it was easier for them to just use the existing wiring and do this in an extra terminal in the wiring centre.

Hopefully I've figured it out correctly. If anyone could verify I'd be most grateful!

 

[RandomGrinch]

Boiler live goes to 1 rather than 8

The switched live to the boiler is the important one to note, and that still goes to 8.

An extra wire goes to 9 from boiler

This is the switched pump connection from the boiler.
It allows the pump to overrun, after the call for heat has ended.

• 1 to nest L, 2 and 5
• 2 to nest N
• 4 to nest 3 (Old timer 4 to nest 3)
• 7 to nest 4 (Old timer 1 to nest 4)
• 6 to nest 6 (Old timer 3 to nest 6)
• Remove old stat wires connected to 2, 4 and 5

Looks ok to me!

Connect 4 and 5 ?? in pink

Or you could just connect 3 from the Nest, to terminal 5 in the wiring centre!

Plus, you've shown it on the diagram, the Heat Link requires an earth connection, if T1 & 2 are used to power the thermostat.