I want to replace my old Honeywell room thermostat with a Drayton
Digistat 3 programmable unit but I'm not sure about the wiring
connections. Both have numbered connectors but I don't know if the
numbering convention is the same. On the Honeywell the connections a
1- Red
2- Blue
3- Yellow
Do I just connect these to the ame numbered terminals on the Drayton
unit?

In article .com,
keith wrote:
I want to replace my old Honeywell room thermostat with a Drayton
Digistat 3 programmable unit but I'm not sure about the wiring
connections. Both have numbered connectors but I don't know if the
numbering convention is the same. On the Honeywell the connections a
1- Red
2- Blue
3- Yellow
Do I just connect these to the ame numbered terminals on the Drayton
unit?

No. Old type mechanical thermostats have a mains heated shunt coil and
need a neutral. This should be taped up out of the way. If you connect it
to the new stat you're likely to blow it up at worst.

Your new stat has a semiconductor temperature sensor which is much more
accurate, is battery operated, so only has a line in and switched out.

It *should* be the blue which is the neutral and has to be be taped up,
but this isn't guaranteed. Can you check at the boiler, etc?

--
*Do paediatricians play miniature golf on Wednesdays?

Dave Plowman London SW
To e-mail, change noise into sound.

In an earlier contribution to this discussion,
keith wrote:

I want to replace my old Honeywell room thermostat with a Drayton
Digistat 3 programmable unit but I'm not sure about the wiring
connections. Both have numbered connectors but I don't know if the
numbering convention is the same. On the Honeywell the connections
a 1- Red
2- Blue
3- Yellow
Do I just connect these to the ame numbered terminals on the Drayton
unit?

I assume that the Drayton unit came with some installation instructions and
wiring diagrams etc.? Have you *read* them?

You need to determine the *function* of each of the 3 wires going to the
original stat, and connect the appropriate wires to the new unit. It is
potentially dangerous to make assumptions based just on colour - unless you
installed it yourself - so you need to find the other end of each of the
wires, and see what it is connected to.

The most *likely* scenario - but not guaranteed - is that the wires a
Red - live feed from the programmer when CH is on
Blue - neutral, used as a return for the accelerator heater in the existing
stat
Yellow - switched live, which turns on a zone valve or boiler and/or pump
depending on what type of system you have

If this *is* the case, you'll only need the red and yellow wires, since
electronic stats don't use accelerator heaters. The terminals to use are
Common plus whichever other one is connected to common when the room
temperature is below the set temperature. Do *not* connect neutral to
anything - insulate the end of the wire and make it safe. If you *do*
connect it to the 'spare' terminal, you'll have a dead short across the
mains - and a very big expensive bang - when the stat switches!
--
Cheers,
Roger
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Hi, Thanks for this. The Drayton unit did come with instructions but it
defines the connections as:
1 - Common
2 - Heating satisfied
3 - Call for heat
My problem is I don't know how these relate to the wires going into the
Honeywell

In article .com,
keith wrote:
Hi, Thanks for this. The Drayton unit did come with instructions but it
defines the connections as:
1 - Common
2 - Heating satisfied
3 - Call for heat
My problem is I don't know how these relate to the wires going into the
Honeywell

Assuming you have found which is the neutral and insulated/isolated it out
of the way, the other two to 1&3. Doesn't matter which to which.

--
*(on a baby-size shirt) "Party -- my crib -- two a.m

Dave Plowman London SW
To e-mail, change noise into sound.