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2 wire - 3 wire - no volts Room Thermostats - Please help!


 
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JimmyKeeley

from United Kingdom

Joined: 17 Sep 2004
Posts: 13
Location: United Kingdom

PostPosted: Wed Feb 24, 2010 1:01 pm Reply with quote

Hi, I have a Baxi Solo 3 Boiler with a Danfoss programmable timer running central heating and hot water.

In the Hall, I have a Danfoss RMT230 thermostat (manual turndial type)

I wish to change the thermostat to a programmale type but the ones I look at all have 2 wire setup. I often see no volts too, what does that mean?

The Danfoss I have is 3 wires. Is there a programmable LCD display room thermostat suitable for my requirements.

Many thanks
Jimmy
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stem

from United Kingdom

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PostPosted: Wed Feb 24, 2010 1:36 pm Reply with quote

Old mechanical thermostats have three wires, a live from the programmer, a switched live out to the motorised valve or boiler, and a neutral. The neutral is there to operate, (in conjunction with the switched live), a little heater called an accelerator, inside the thermostat to improve the accuracy of old mechanical moving components. New electronic thermostats don't need the accelerator and so don't always need a neutral, hence only 2 wires. If they have a display it's battery operated so that it remains visible when the programmer switches off the supply to the thermostat.

The "no voltage" is where a mains supply, live and neutral is used by the thermostat to switch an integral relay (electric switch) the contacts in the relay are not connected to the mains supply to the thermostat, so they are voltage, or potential free.

So because you have three wires available for use, you can have either sort. Just isolate the neutral if you don't need it.

When you've chosen your new thermostat post again if you have any questions.
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JimmyKeeley

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Joined: 17 Sep 2004
Posts: 13
Location: United Kingdom

PostPosted: Wed Feb 24, 2010 5:15 pm Reply with quote

Thank you for the reply, Im glad I am not limited due to the extra wire.

I was looking at the Phaseliner TS930 which states a 3 wire but I dont understand the diagram. Or a different one if you know of a better one that will show current temp along with set temp etc.

My current stat (RMT230) has Blue wire to 4, Red to 1 and Yellow to 2

I have included diagram for both stats.

{EDIT} - Have found this RMT230 image to be incorrect as its not UK version - UK version is shown in later post as 230v




Would it be Blue 1, Yellow 2 and Red 3?

Many thanks
Jimmy


Last edited by JimmyKeeley on Mon Mar 01, 2010 10:48 pm, edited 1 time in total
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stem

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PostPosted: Thu Feb 25, 2010 8:40 am Reply with quote

I'm a bit puzzled by your diagram of the RMT 230. Can I assume that you've found it on the web somewhere and that it doesn't relate to your system. This is because of the reference to 24V. All of the Baxi Solo 3's I've seen have a 230VAC live from the controls, and I don't know what a TWA is. (some type of "actuator" possibly with a nc (normally closed) contact?) You can also see the accelerator heater marked 'Rp' in the diagram too, but, unless it's designed to operate on 24v, a normal 230v accelerator won't emit much heat with 24v.

I think you need to check that you actually have 230v across the red & blue, otherwise the Phaseliner TS930 won't work.

Assuming you do have 230v, Blue 1, Yellow 2 and Red 3 is correct as you have worked out.
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JimmyKeeley

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PostPosted: Thu Feb 25, 2010 10:34 am Reply with quote

the RMT230 diagram is fom the Danfoss website. Im not sure about the voltage, I will try to find out.

Many thanks
Jimmy
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D_Hailsham

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PostPosted: Thu Feb 25, 2010 12:11 pm Reply with quote

The RMT230 is the mains voltage version. The RMT24 is the low voltage, aka volt-free, version.

Phaseliner do not make stats, they just stick their badge on someone else's product. You would be do much better buying a reputable make, such as the Honeywell CM907 or CM927 if you want a wireless stat.
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JimmyKeeley

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Joined: 17 Sep 2004
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Location: United Kingdom

PostPosted: Sat Feb 27, 2010 11:12 pm Reply with quote

Thats great, I may have to go with the CM907

Many thanks
Jimmy
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stem

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PostPosted: Mon Mar 01, 2010 8:28 am Reply with quote

D_Hailsham wrote:
The RMT230 is the mains voltage version. The RMT24 is the low voltage, aka volt-free, version.

That's what puzzled me about the above diagram, it's entitled RMT230 (ie mains version), but the wiring is labeled 24v.
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JimmyKeeley

from United Kingdom

Joined: 17 Sep 2004
Posts: 13
Location: United Kingdom

PostPosted: Mon Mar 01, 2010 10:34 pm Reply with quote

just checked the internet again, seemed I copied diagram for the non UK version. Apologies for my ignorance!

icon_redface.gif Just as well Im not an electrician!! icon_redface.gif

This is diagram for UK version


I wanted the Honeywell Decor but thats an American thermostat so I will go for the CM907 as recommended which does from 24v - 230v anyway.

Many thanks
Jimmy
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JimmyKeeley

from United Kingdom

Joined: 17 Sep 2004
Posts: 13
Location: United Kingdom

PostPosted: Sat Mar 06, 2010 2:24 pm Reply with quote

Honeywell CM907 purchased - installed and working perfectly.

Many thanks for all your help
Jimmy
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stem

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PostPosted: Sat Mar 06, 2010 7:51 pm Reply with quote

Excellent! glad to hear it icon_biggrin.gif and thanks for the update.
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