Wire a thermostat to an existing light switch

ma11achy

Hi all,

I recently purchased two Heatmiser DS1-L digital thermostats to replace my old Horstmann HRT3's.
The problem I have is that the Horstmann stats are two wire and the ones I purchased are three wire.

The old Horstmann have a live and a neutral, the neutral I suspect also acts as the switch to turn on and off the Oil heating system (three zone, electronic valve controlled).

The DS1-L's require a Live, Neutral and a third wire to tell the heating system to shut on/off.

As I only have two wires leading to the thermostat controls, I'd like to know if it would be ok to take a live and a neutral in parallel from a light switch beside the thermostat and use these to connect a live and neutral to the DS1-L.

I could then connect the thermostat neutral (which I referred to above as the suspected switch control for the heating) to the control connection on the DS1-L.
The unused Live to the thermostat control I would then tape off and leave disconnected.

What do you think - is this doable?

Many thanks,
Martin.

Bruthal

ma11achy wrote: »

Hi all,

I recently purchased two Heatmiser DS1-L digital thermostats to replace my old Horstmann HRT3's.
The problem I have is that the Horstmann stats are two wire and the ones I purchased are three wire.

The old Horstmann have a live and a neutral, the neutral I suspect also acts as the switch to turn on and off the Oil heating system (three zone, electronic valve controlled).

The DS1-L's require a Live, Neutral and a third wire to tell the heating system to shut on/off.

As I only have two wires leading to the thermostat controls, I'd like to know if it would be ok to take a live and a neutral in parallel from a light switch beside the thermostat and use these to connect a live and neutral to the DS1-L.

I could then connect the thermostat neutral (which I referred to above as the suspected switch control for the heating) to the control connection on the DS1-L.
The unused Live to the thermostat control I would then tape off and leave disconnected.

What do you think - is this doable?

Many thanks,
Martin.

The neutral on them digital stats is just to power the actual stat electronics because the stat needs a live and neutral to power its electronics, so you will have a live in, and live out just like you do on the original stats, but the live out may be blue by the sound of it on your original ones but is not a neutral, and a neutral is now needed at the (new)stat just to power the stat which is electronically controlled, where as your other ones are just a mechanical switch. I would not be going near any lighting circuits anyway. You may need electrician to sort that properly.

What you are saying will not work so dont try it, get the professional in.

2011

The old Horstmann have a live and a neutral, the neutral I suspect also acts as the switch to turn on and off the Oil heating system (three zone, electronic valve controlled).

No offense intended but to me this statement shows demonstrates that you do not have a proper understaning. Please do as Robbie says and get a qualified electrician.

As I only have two wires leading to the thermostat controls, I'd like to know if it would be ok to take a live and a neutral in parallel from a light switch beside the thermostat and use these to connect a live and neutral to the DS1-L.

No this would not be a good idea. It would not be normal to have a neutral at a light switch anyway.

Here is a link showing the connection details:
http://www.heatmiser.co.uk/support/admin/attachments/ds1l_manual.pdf

M cebee

re-wiring will 'prob' be too much hassle

you'll prob have to replace like for like ie: 2 -wire stats

ntpm

You should not take a neutral from the light circuit... or any other circuit.

If your controls have been wired correctly they should be supplied from a independent circuit via a double pole switched fused spur( 3or5 Amp).
This gives full Live and Neutral for safe issolation and safety.It must have suitable fused protection.
if you take a neutral from and other circuit you can get backfeed when main isolator if switch off.

As stated in earlier threads your original stst was acticing as a switch... Two cables are Live in, switch live out. that fact that one cable is blue it does not make it a Neutral... electrician was too lazy to run correct colours or even retag with tape.

The new stat requires 3cables Live In, Switch Live Out, and Neutral.

So you need to run a neutral from the original controls junction box.

ma11achy

Great stuff, thanks ntpm, that's made perfect sense. I'll go ahead and purchase a two wire stat and sell the others on eBay.

Cheers,
Martin.