Thermostat envy

[adey]

Hi,

A mate of mine has a Honeywell CM907 programmable thermostat which makes my Horstmann HRT2 look very inadequate!! Besides that, the HRT2 might as well be replaced with an on/off switch for all the use it is.

I have a BAXI Combi 105 HE boiler which has a mechanical timer but I want to put the boiler on constant and use a 7 day programmable thermostat like the CM907. However I believe this is battery powered with two wires from the boiler whereas the HRT2 is mains fed with three wires (according to the spec sheet i've read).

So, my question is: Does anyone know if the CM907 is compatible with my setup OR can anyone recommend a suitable replacement for the HRT2 with similar features to the CM907?

cheers
Adey

 

[ChrisR]

Sure, easy.
You'll just need terminals A and B, tape up the old neutral or earth, whichever it was.

 

[adey]

Thanks Chris. Easy when you know how

Shopping time....
adey

 

[Agile]

Its important that you get the connections right otherwise you could do damage!

In many cases they have used red and yellow as the switched wires and blue as the neutral.

BUT the installer could have used anything as well as using an earth wire as a neutral ( or even live ) conductor.

If its not obvious then you should use a neon screwdriver to identify which two wires are both live with thermostat in the "on" mode.

Alternatively and better is a test meter between a terminal and a seperate earthed item such as a radiator or a fixing screw on a properly connected socket. ( But earlier wiring did not always earth the metal box behind and sometimes plastic boxes were used ).

Its quite simple really with a bit of knowledge but the opportunities for DIY mistakes abound!

Tony

 

[meadowhog]

I've just fitted heatmiser PRT/HW. Its a 3 wire so no need for batteries.It will also control the hot water if wires can be fed to it. Its currently wired into the old time controller which is set to constant but the old controller can be thrown at a later time.

Best of all for some reason on Amazon its dirt cheap. Maybe a typo so I ordered 3.

 

[adey]

Tony, cheers for the warning!

 

[PEDANTICVINDICTIVEMAN]

Never ever rely on a neon screwdriver to test for anything, "always" use a multimeter, they should be banned.

 

[adey]

Sure, easy.
You'll just need terminals A and B, tape up the old neutral or earth, whichever it was.

I've now bought the CM907 and understand I need to wire up A and B, I'm just not sure which wires to use. The link below shows how the unit is wired, so which of the wires 1, 3 and 4 do I wire to A and which to B and which to tape up?

http://www.horstmann.co.uk/download.../ThermoStats/HRT2UserandInstallationGuide.PDF

 

[mikely]

1 to A, 3 to B, 4 tape up. It's the neutral connection that is not needed.

 

[aptsys]

Don't use tape FFS!

 

[londonboy]

Use a small connector block.. absolutely no tape and no cutting off!!

I am very surprised a neon screwdriver was suggested