Wiring a Honeywell T6360 thermostat

[QuestionQuigley]

I'm replacing an old Honeywell thermostat with a T6360. The old one has four wires as shown:

Old

• QuestionQuigley
• 22 Nov 2020

Old thermostat

This is the wiring diagram for the old one:

Old_Wiring_Diagram

• QuestionQuigley
• 22 Nov 2020

Old thermostat wiring diagram

So the terminal numbers/wire colours reading bottom-to-top are:
1: Brown
4: White
3: Green/yellow
2: Blue

The wiring diagram for the T6360 is:

New_Wiring_Diagram

• QuestionQuigley
• 22 Nov 2020

New thermostat wiring diagram

This shows only three wires rather than the four I have. It seems obvious that Brown (Live) should go to terminal 1 and Blue (Neutral) to terminal 2. But I'm unclear on the other two wires, especially as the green/yellow one - which I'd normally expect to be Earth - appears not to be used as Earth here.

Given that the two units are both Honeywell, is it OK to just go with the same set-up. i.e. white to terminal 4 and green/yellow to terminal 3?

 

[MeldrewsMate]

The equivalent function would be realised by doing what you suggest, however I strongly suggest you change it so that the white wire replaces the green/yellow wire (at both ends), and the green/yellow is used solely for the protective earth.
In addition it's wise to sleeve the switched live wire (from terminal 3) with a brown marker.

 

[ianmcd]

Best to trace where the existing white wire is going to, it is unusual to have a wire in the CH satisfied terminal , but it is possible that you have what is called a MOMO zone valve on the heating

 

[stem]

It's a straight swap, the diagrams you posted show that the terminals of the old and new thermostats have exactly the same function number for number [1 is live, 2 is neutral, 3 is switched live]

However, it's unusual that there's a wire connected to terminal 4. This terminal is only made live when there is no demand for heating, so it could mean:

1. There is some sort of cooling device / air-conditioning attached to it.

2. You have a very rare heating system with what is known as a MOMO valve controlling it.

3. The wire isn't connected to anything useful at the other end and terminal 4 has just been used to 'park' the wire.

The only way to confirm for sure, would be by knowing what is connected to the other end of each of the wires. Unfortunately the colours of wires are meaningless as they would have been chosen by the original installer and as earlier posts show some don't always make a sensible choice. It's what is connected to each end of a wire that determines its function, not the colour of its insulation.

Edit
Sorry @ianmcd I missed your original post must have come in whilst I was having breakfast, so I seem have repeated what you had already written. Only using a lot more words

 

[ianmcd]

It's a straight swap, the diagrams you posted show that the terminals of the old and new thermostats have exactly the same function number for number [1 is live, 2 is neutral, 3 is switched live]

However, it's unusual that there's a wire connected to terminal 4. This terminal is only made live when there is no demand for heating, so it could mean:

1. There is some sort of cooling device / air-conditioning attached to it.

2. You have a very rare heating system with what is known as a MOMO valve controlling it.

3. The wire isn't connected to anything useful at the other end and terminal 4 has just been used to 'park' the wire.

The only way to confirm for sure, would be by knowing what is connected to the other end of each of the wires. Unfortunately the colours of wires are meaningless as they would have been chosen by the original installer and as earlier posts show some don't always make a sensible choice. It's what is connected to each end of a wire that determines its function, not the colour of its insulation.

Edit
Sorry @ianmcd I missed your original post must have come in whilst I was having breakfast, so I seem have repeated what you had already written. Only using a lot more words

No problem @stem is all I can think of why the wire would be there