Replacing Room Thermostat 3 wires to 2 wires??

[Harvest Fields]

Thanks for the help guys!

Now i just need to calibrate the target temp so the heat level is just right...why do they insist on putting room thermostats in hall ways where is probably one of the more coldest areas of a house!??

Hold on. So was there an issue or not mate?

 

[BlockABoots]

So you have stated above that the flame symbol. Which is the symbol that shows the stat is calling for heat or not goes off then there is no issue. Unless you are talking about something else?

No you misunderstand.....

When the target temp of the thermostat is set higher than the current room temp the flame is displayed as its calling for heat and the boiler fires up to reach the target temp.

If i set the thermostat target temp lower than the current room temp than the flame disappears and the boiler goes off. This as it stands is all operating as it should do.

But what i did notice that if i turned the heating off from the CP then the flame icon on the thermostat was still being display as it was still calling for heat as the thermostat hadn't reach its target temperature. I was questioning weather the thermostat should still be displaying the flame even though the heating was turned off via the CP, but as Ric2013 pointed out the thermostat isnt advanced enough to know that the CP has switched the heating off.....im guessing if i wanted an intelligent enough thermostat for that i would have to spend more than the £30 i paid for this honeywell one!

 

[Harvest Fields]

Ohhhh. Makes sense now.

 

[Ric2013]

To answer your question on why the stat is generally in the hallway, it is because the hall is generally the last to warm up. If you put a stat in a living room then the living room might warm up first and will be nice and warm, but the rest of the house might still be cold.

I personally dislike this practice, as it assumes that the entire house needs to be heated when, in my opinion, 14°C in a corridor is sufficient for most people, but if the heating has been off and the entire house is at 14°C, then the living rooms will be too cold. This is why I personally prefer multizone systems (or use a wireless stat that you can move around).

In fact, I would argue that a pneumatic time switch that stays on for half an hour after you push it in could be the most energy-efficient stat. When you are cold, you turn it on; when you aren't cold, you simply forget it and the heating goes off again. But then, I am quite alternative in my thinking.

 

[DevsAd]

Blimey, BlockABoots - two pages to get the answer you were after. And you basically worked it out for yourself...

(You were initially confused by that 'neutral' on the diagram seemingly connected to 'B'. But if you look at the diagram again, you'll see that there's a rectangular 'block' on that line coming out of 'B', and that's the boiler, and the 'neutral' is actually connected to the other side of that rectangle! In other words, when your stat closes its contacts inside (when it's calling for heat) the LIVE that's going 'in' 'A' then comes 'out' of 'B' and goes in to one side of the boiler (rectangle). It's then the other side of the boiler that's effectively connected to the neutral. Make sense?)

Anyhoo, that's one issue. The other is the wee 'flame' symbol coming on. The new 'stat is battery operated so works independently of everything else. It hasn't a clue what the rest of the system is doing. It doesn't know if the programmer/timer is on or off. It doesn't know if the boiler is running , or even if it's fallen off the wall.

All it knows - in its isolated, battery-powered world - is whether the temp it is sensing in the air is higher or lower than the temp it's been asked to provide. That's it. If the air is too cold, the wee 'flame' comes on and the two contacts inside close. Once the temp is reached, the flame goes off and the contacts open.

That's it. If your house blew up in a gas explosion - I hope it won't - then amongst the rubble will lie a wee detached DT90 which will still show a flame symbol if it's too cold.

A thought - hadn't you considered a programmable room stat?

 

[Stoney Ground]

I have he same problem mate. Sometimes I am midpost, then I get distracted by the kids or the missus and by the time I actually post someone has beaten me to it.

Roughly translated “I have sausage fingers and keep hitting the wrong keys”

 

[fixitflav]

Hmm actually looking on the mounting plate of the new thermostat it does actually require neutral and not live out/switching as i was told..
The thermostat doesn't require neutral. A is live, the contacts are changeover, B normally open (closed when calling for heat), C normally closed, but not used in this case. The N is the neutral of the heating system, remote from the 'stat. The system is represented by the rectangle.

https://i.*********/UTyPeNY.jpg

so it needs live (red) and neutral (blue) ???

 

[kozak1968]

It always amazes me how many replies a roomstat gets. Call a professional if in doubt... Second thoughts just call a professional!

 

[Ric2013]

I'm still amazed that on the same forum that whenever anyone mentions gas the stock answer is we won't help because it'd be illegal and dangerous for someone not competent to do the task, I think I'm the only one that has ever mentioned electrical work being a similar matter.

Although, yes, big deal, he's replacing a thermostat, surely electricity, like gas, can be a matter of safety and legality as well?

It is worth noting, however, that since 2013, in England, control wiring for central heating is no longer considered as notifiable work, and so can be legally carried out by amateurs without the need for professional testing (in Wales, central heating control wiring remains notifiable). This does not mean that it need not be tested. Whether notifiable work, as defined in the building regulations, or not, electrical work must be tested to BS7671, which few amateurs will be able to do, through lack of equipment if nothing else.