Following the advice here, I picked up a Horstmann DRT2 programmable 'stat, to replace the Danfoss RT230 I had ...
Just a quick Q about the wiring ... the RT230 has a red (Live ?) going to terminal 4, and a blue (neutral ?) going to terminal 1. Looking at the DRT2 instructions, they say Live should go to "COM" and Neutral to "NO".
So red wire goes to "COM" and blue to "NO" - and we're off ?
I cannot find an RT230, but it looks like the RT series have a neutral connection for hysteresis heater. Are you sure there are not three wires (excluding any earth) connected to the old stat?
The DRT2 instructions do not say to connect the neutral to "NO". It is battery powered so only needs two wires, live feed and switched live feed to boiler/pump. Any neutral should be insulated. he live wire goes to COM and the switched feed to the boiler goes to "NO"
If there are only two wires to your existing stat, then in all probability they are live and switched live.
Not sure what you mean ? I checked the connections to the old 'stat, and sure enough, when it was "on" the live and switched live terminals were closed circuit. When I twiddled the dial and the 'stat went off, they went open circuit.
Like I said, I tested it as is, and it works spot on ... so not sure what else I should do with the blue wire (and in response to the usual jokers, it could be a bit scratchy :) )
Ah, just found
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shows the blue wire I had, which went to "4" did indeed power the little heater.
I think what Adam means is that using the earth conductor for the switched live is "poor form" and if you can use the now spare blue wire as the switched live (Sleeved at the end with a red sleeve) it would be a "proper job". The original thermostat should have been connected with a cable having three wires plus earth, but the installer did it on the cheap with presumably what was to hand.
Ah, I did wonder. The heating system was completely gutted and replaced in 2002, and I had no part in it at all (it was a recommended plumber who subbed out the electrics). I shall have a little shufty and see if I can amend it to be "nice".
But there is now a mystery. The OP said that he had the work done in 2002, now thats pre colour change.
So there would only be a blue wire if it is a flex or a 3 core and earth. I wonder if Jethro means that the yellow core of a 3 core and earth was used as the switched live?
OK ... here's what I have now ... 3 core + uninsulated wire. Blue (which went to the "4" connection on the old 'stat) - now disconnected & insulated
Red - (was connected to "1") goes to "COM" on new 'stat
Yellow with red sleeve (went to "2" on old 'stat) now goes to "NO"
Uninsulated wire - still goes to metal backbox (although neither stat was in the box, but over it)
As I said I had to refresh my memory of hysteresis (fond memories of programming a robot crane to swing a weight with zero recoil, and an assembler program to drive a heater and fan assembly) to understand why there was a neutral connection. But having removed the old stat, I confirmed it was switching 1 and 2, which are the wires I reused.
Bloody hell, I think we got there. I only answered my own post to archive this in case anyone else has the same job to do. Thanks as always guys - please have a virtual pint on me !
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