Our central heating thermostat went kaput. It is a simple Honeywell
T40 and it is a "two-wire" item.

I couldn't get a direct replacement so chose a Siemens RAA20 which is
also a "two-wire" item.

So far, so good. But on opening up the broken Honeywell, while the
wiring diagram inside the cover shows two incoming wires, L and N, the
wire from the controller has *four* cores and they are all connected.

Green/yellow goes to earth terminal (E). Blue goes to neutral
terminal (2). Yellow goes to terminal 3. Red goes to live terminal 1.

So I thought to myself, how can this be a "two-wire" item?

Just to complicate matters, the replacement Siemens RAA20 is also
described as a "two-wire" item, but it has *three* terminals. L is
clearly live, but there are two other terminals Y1 and Y2.

Now I am totally confused. Can anyone please tell me which of the
four original wires (red, blue, yellow/green and yellow) goes to which
of the three terminals of the "two-wire" Siemens RAA20?

Please help! It's getting cold in here!

Tony Polson wrote:

Our central heating thermostat went kaput. It is a simple Honeywell
T40 and it is a "two-wire" item.

I couldn't get a direct replacement so chose a Siemens RAA20 which is
also a "two-wire" item.

So far, so good. But on opening up the broken Honeywell, while the
wiring diagram inside the cover shows two incoming wires, L and N, the
wire from the controller has *four* cores and they are all connected.

Green/yellow goes to earth terminal (E). Blue goes to neutral
terminal (2). Yellow goes to terminal 3. Red goes to live terminal 1.

So I thought to myself, how can this be a "two-wire" item?

Just to complicate matters, the replacement Siemens RAA20 is also
described as a "two-wire" item, but it has *three* terminals. L is
clearly live, but there are two other terminals Y1 and Y2.

Now I am totally confused. Can anyone please tell me which of the
four original wires (red, blue, yellow/green and yellow) goes to which
of the three terminals of the "two-wire" Siemens RAA20?

Please help! It's getting cold in here!


Siemens RAA20 wiring diagram is at:
http://www.sbt.siemens.com/HVP/Compo...tion/RAA20.pdf

Tony Polson wrote:

Tony Polson wrote:

Our central heating thermostat went kaput. It is a simple Honeywell
T40 and it is a "two-wire" item.

I couldn't get a direct replacement so chose a Siemens RAA20 which is
also a "two-wire" item.

So far, so good. But on opening up the broken Honeywell, while the
wiring diagram inside the cover shows two incoming wires, L and N, the
wire from the controller has *four* cores and they are all connected.

Green/yellow goes to earth terminal (E). Blue goes to neutral
terminal (2). Yellow goes to terminal 3. Red goes to live terminal 1.

So I thought to myself, how can this be a "two-wire" item?

Just to complicate matters, the replacement Siemens RAA20 is also
described as a "two-wire" item, but it has *three* terminals. L is
clearly live, but there are two other terminals Y1 and Y2.

Now I am totally confused. Can anyone please tell me which of the
four original wires (red, blue, yellow/green and yellow) goes to which
of the three terminals of the "two-wire" Siemens RAA20?

Please help! It's getting cold in here!


Siemens RAA20 wiring diagram is at:
http://www.sbt.siemens.com/HVP/Compo...tion/RAA20.pdf

And the Honeywell wring diagram (it is a T6360B not a T40) is at:
http://content.honeywell.com/uk/homes/FAQ/tstat.pdf

"Tony Polson" wrote in message
...
Our central heating thermostat went kaput. It is a simple Honeywell
T40 and it is a "two-wire" item.

I couldn't get a direct replacement so chose a Siemens RAA20 which is
also a "two-wire" item.

So far, so good. But on opening up the broken Honeywell, while the
wiring diagram inside the cover shows two incoming wires, L and N, the
wire from the controller has *four* cores and they are all connected.

Green/yellow goes to earth terminal (E). Blue goes to neutral
terminal (2). Yellow goes to terminal 3. Red goes to live terminal 1.

So I thought to myself, how can this be a "two-wire" item?

Just to complicate matters, the replacement Siemens RAA20 is also
described as a "two-wire" item, but it has *three* terminals. L is
clearly live, but there are two other terminals Y1 and Y2.

Now I am totally confused. Can anyone please tell me which of the
four original wires (red, blue, yellow/green and yellow) goes to which
of the three terminals of the "two-wire" Siemens RAA20?

You might need to do a little self help until someone with the specific
answer comes along but this is what's happenning. The neutral is sort of
"optional" just helps the stat work better, the earth is self explanatory,
one of the wires (U test) is a live or timed live and the one that's left is
the stat switched live to the boiler. Guessing that Y1 and Y2 might be NO
and/or NC contacts. You want NO.

HTH

Jim A

"Tony Polson" wrote in message
...
Tony Polson wrote:

Our central heating thermostat went kaput. It is a simple Honeywell
T40 and it is a "two-wire" item.

I couldn't get a direct replacement so chose a Siemens RAA20 which is
also a "two-wire" item.

So far, so good. But on opening up the broken Honeywell, while the
wiring diagram inside the cover shows two incoming wires, L and N, the
wire from the controller has *four* cores and they are all connected.

Green/yellow goes to earth terminal (E). Blue goes to neutral
terminal (2). Yellow goes to terminal 3. Red goes to live terminal 1.

So I thought to myself, how can this be a "two-wire" item?

Just to complicate matters, the replacement Siemens RAA20 is also
described as a "two-wire" item, but it has *three* terminals. L is
clearly live, but there are two other terminals Y1 and Y2.

Now I am totally confused. Can anyone please tell me which of the
four original wires (red, blue, yellow/green and yellow) goes to which
of the three terminals of the "two-wire" Siemens RAA20?

Please help! It's getting cold in here!


Siemens RAA20 wiring diagram is at:
http://www.sbt.siemens.com/HVP/Compo...tion/RAA20.pdf


OK, posted already but first post isn't showing yet. Got the data sheet
now, L is Live obviously or hopefully your timed live. Y1 is the
switched(timed) live back to the boiler, Y2 is for cooling, leave
unconnected. This stat doesn't need a neutral.

Jim A

"Tony Polson" wrote in message
...
Tony Polson wrote:

Tony Polson wrote:

Our central heating thermostat went kaput. It is a simple Honeywell
T40 and it is a "two-wire" item.

I couldn't get a direct replacement so chose a Siemens RAA20 which is
also a "two-wire" item.

So far, so good. But on opening up the broken Honeywell, while the
wiring diagram inside the cover shows two incoming wires, L and N, the
wire from the controller has *four* cores and they are all connected.

Green/yellow goes to earth terminal (E). Blue goes to neutral
terminal (2). Yellow goes to terminal 3. Red goes to live terminal 1.

So I thought to myself, how can this be a "two-wire" item?

Just to complicate matters, the replacement Siemens RAA20 is also
described as a "two-wire" item, but it has *three* terminals. L is
clearly live, but there are two other terminals Y1 and Y2.

Now I am totally confused. Can anyone please tell me which of the
four original wires (red, blue, yellow/green and yellow) goes to which
of the three terminals of the "two-wire" Siemens RAA20?

Please help! It's getting cold in here!


Siemens RAA20 wiring diagram is at:
http://www.sbt.siemens.com/HVP/Compo...tion/RAA20.pdf

And the Honeywell wring diagram (it is a T6360B not a T40) is at:
http://content.honeywell.com/uk/homes/FAQ/tstat.pdf


gee this NG is slow tonight.

hopefully you have worked it out already, Honeywell (1) is Siemens (L),
Honeywell (3) is Siemens (Y1), .....err thats it. see just 2 wires.

Jim A

"Jim Alexander" wrote:


"Tony Polson" wrote in message
.. .
Our central heating thermostat went kaput. It is a simple Honeywell
T40 and it is a "two-wire" item.

I couldn't get a direct replacement so chose a Siemens RAA20 which is
also a "two-wire" item.

So far, so good. But on opening up the broken Honeywell, while the
wiring diagram inside the cover shows two incoming wires, L and N, the
wire from the controller has *four* cores and they are all connected.

Green/yellow goes to earth terminal (E). Blue goes to neutral
terminal (2). Yellow goes to terminal 3. Red goes to live terminal 1.

So I thought to myself, how can this be a "two-wire" item?

Just to complicate matters, the replacement Siemens RAA20 is also
described as a "two-wire" item, but it has *three* terminals. L is
clearly live, but there are two other terminals Y1 and Y2.

Now I am totally confused. Can anyone please tell me which of the
four original wires (red, blue, yellow/green and yellow) goes to which
of the three terminals of the "two-wire" Siemens RAA20?

You might need to do a little self help until someone with the specific
answer comes along but this is what's happenning. The neutral is sort of
"optional" just helps the stat work better, the earth is self explanatory,
one of the wires (U test) is a live or timed live and the one that's left is
the stat switched live to the boiler. Guessing that Y1 and Y2 might be NO
and/or NC contacts. You want NO.

HTH


Many thanks, Jim.

I followed your suggestions and it works fine. Thanks again.