Advice required - relay wiring for thermostat control

Curious. The "RWG" standard that the thermostat uses originated with 24V heating systems in the USA

Here is a attempt at what I think you will need:

Your original pic shows your original thermostat with terminals;
C
R
W1
G
Y
W2

I'm pretty sure W1, W2 are the 2 stages of heating.

I'm then going to GUESS that R = Red = +24V (as suggested by Alan).

G is most likely FAN.

Which leaves C and Y. I'm guessing that Y is cool, and C... not sure, if this goes to the outdoor unit it could be pump or dump (or combo) depending on the outdoor unit. It could also be GROUND or COMMON.

Lets assume for now that we have:

R = Red = +24V
G = FAN
W1 = Heat stage 1
W2 = Heat stage 2
Y = Cool
C = ???

Then you need to duplicate that arrangement using a cbus relay (because your cbus thermostat is the model w/o relays).

If you look in the link posted by Newman for the thermostat manual, and check figures 7, 8, 9, 10, 11 then I think you will be getting close.

Fig 9 in particular is a big hint - substitute the Heat Pump cooler for an evap unit and its starting to look similar.

Looking at your Lennox wiring diagrams, fig 10 - this confirms that W2 is used for 2nd stage heating. If you don't want to use that then don't connect it.

Looking at Fig 13 of the Lennox manual, it appears to be a horrible amalgam of the external box wiring, as well as the internal schematic wiring shown in the bottom right hand side, with the room thermostat shown as S1.

This SEEMS to show:
R = a common input to the room stat, sourced from 24V (yay, 1 guess correct)
W1, W2 = heating (another guess correct)
Y = cooling - goes to the main box but is not connected there, so on the main box its a looping terminal that then goes to the outdoor unit
G = much the same as Y... another looping terminal to the outdoor unit
C = ground

Exactly HOW those terminals make the unit operate is not very clear from the diagram but seems like we're on a moderately sensible track here.

NOW THAT HARD PART.

You show your cbus relay with terminals a, b for each relay. You have basically duplicated the connections from the original thermostat room unit to terminals on a cbus thermostat.

That won't work.

You need to check the Lennox manual, fig 13. Look at "S1 Room Thermostat" in the middle of the right hand side.

You will see that R is a common which you will need to wire to the "A" side of 4 relays (you only need 4, not 5).

Then wire the "B" side of relay 1 to "W1".
Then wire the "B" side of relay 2 to "W2".
Then wire the "B" side of relay 3 to "Y".
Then wire the "B" side of relay 1 to "G".

As far as I can tell you don't need to wire "C" to the cbus relay at all.

Then, program the thermostat so that:
- Fan is "G"
- Cooling is "Y"
- Heat stage 1 is "W1"
- Heat stage 2 is "W2"

This ***should*** do what you want.

Be careful. Check everything. Including what I suggest above. If it all turns to poo don't blame me.