Stumped with a smart stat.

[glenncraig]

Hi all I am new to the group so thanks for letting me join. I am looking for advice on the install of a smart stat.
I have removed my old (very) old stat and have found it only contains a brown, blue and earth wire. I removed the whole unit from the wall to try and find any other wires hidden, but there was none. How on earth can I fit my new stat. My thermostat is in the bottom hall while my combi boiler is upstairs. Here are some pics of the offending items. Thank you all in advance.

 

[glenncraig]

Sorry here is the pic of the new stat it wouldn’t post 1st time

 

[ericmark]

So the thermostat is for underfloor heating? Not sure if the NTC needs compensating cable or if twin and earth will work, or if the remote sensor is for the floor or if it allows the thermostat and sensing elements to be remote from each other.

With many "Smart" thermostat the dial and sensor are wireless or single pair of 12 volt wires connected to base/heat link/or other name, so not sure if new thermostat goes where old one was, or just the NTC sensor what does the paperwork say?

 

[ericmark]

I will guess you have picked up wrong thermostat, and you have a under floor heating one which you don't want, so will be returning? So at this point question is what do you want the smart thermostat to do? I hate the word "Smart" in the main it seems to mean it connects to your phone, but what it does then varies so much, my Nest Gen 3 has geofencing (it detects when phone is close to home) and occupancy detect so either will turn heating back up, and it auto turns down when you are not at home, and with the hard wired option you need two wires between the thermostat and heat link, so your heat link would be upstairs and the thermostat where the originally is and it does not need any batteries.

Now the Nest e works very like the Nest Gen 3, but it is all battery operated, so base will go instead of original thermostat, and new thermostat can be put where ever you like.

Some so called "smart" thermostats allow you to alter with phone, but are manual and you have to actually get your phone out to turn heating up or down.

Some are better than Nest and allow you to control each room on its own, and some call the thermostat smart as it uses a mark/space ration to stop it over shooting, which to be frank is not a good idea with a modulating boiler.

There are also thermostats which connect to the ebus of the boiler so they gradually increase or decrease output with near zero hysteresis, some special for boiler, some what is called OpenTherm.

So what do you want the "smart" thermostat to do?

Likely the new one will work, but it will need the cable swapping to a 5 core cable and it does seem a lot of work specially if wrong thermostat to start with.

 

[ianmcd]

If you want to use that thermostat you will have to run a new cable, if you dont want to run a new cable buy a battery powered room thermostat and you can use the existing cable

 

[ianmcd]

So the thermostat is for underfloor heating?

What makes you think it is for underfloor heating ?

 

[glenncraig]

Hi thanks for the response. I do not have underfloor heating, the thermostat was bought to replace my old and allow me to control the heating via Alexa. I only used the term smart as I normally would call it WiFi, but reading through some posts in the forum others were calling them smart thermostat, so rather than cause confusion I thought I would refer to it likewise. I have watched several YouTube videos in the installation of this Identical thermostat but most had either 3 or 4 wires and they worked fine in controlling the central heating. I thought it would be an easy task but as usual nothing goes right.

 

[glenncraig]

If you want to use that thermostat you will have to run a new cable, if you dont want to run a new cable buy a battery powered room thermostat and you can use the existing cable

If I were to run just a new 240v supply from the wall or socket then connect the 2 wires in the old thermostat to the contacts in the new thermostat would that possibly work?

 

[ianmcd]

If I were to run just a new 240v supply from the wall or socket then connect the 2 wires in the old thermostat to the contacts in the new thermostat would that possibly work?

No the live and neutral should come from the same supply as the boiler , it would work but would not conform to the installation instructions for the boiler or the thermostat, you need a minimum of 3 cores and possibly 4 cores if your boiler uses low voltage switching, you only have twin and earth so only 3 cores, I never said you had underfloor heating someone else mentioned it not me, if you cant run a new cable but can return your smart stat, look at nestE has to be the E it is battery powered so you just use the 2 wires already in the existing stat and that will connect to alexa

 

[glenncraig]

Sorry Ian I never meant for you to think I was talking to you about underfloor heating. I saw your reply asking the other chap how he thought it was underfloor heating.
I might be able to run new wires from my boiler to the thermostat. Thanks for your assistance

 

[glenncraig]

If I were to reposition the thermostat to a place just out of the boiler cupboard. What sort of wire would be required to wire straight to the boiler?

 

[ianmcd]

Most heating engineers carry drums of 5 core 0.75mm flex and this is for wiring heating systems, I buy mine in 100M drums but last time I was in B&Q they were selling it by the meter, so if you measure how much you need you wont need to buy a whole drum, or you can use 4 core if it is cheaper

 

[ericmark]

Not sure about line and neutral needing to come from same circuit as boiler if the thermostat is a no volt type? I always would as really you want to switch off one FCU and all is dead, but my house has 10 separate supplies, one 230 volt from FCU and 9 x 3 volt from pairs of batteries.

Terminals 5 and 6 show NTC 10k which I would suspect should go to a sensor to ensure floor does not get too hot, so that why I think it is for under floor electric heating.

As to Alexa hope it is better than Nest Mini, mine with read out room temperatures, but it also gets it wrong, so switch off radio 4 gets reply switching off 5 switches and really not a clue what it has done, using with phone OK, voice commands it's like Stan in the bank advert.

I would forget smart and fit simple programmable two wire so easy to fit and think about 5 temperature changes per day can be programmed. OK I use Nest but it is a tad more expensive.

 

[glenncraig]

Thanks for all your help. I’ll post on my progress when done (if I don’t electrocute myself).

 

[glenncraig]

My Alexa must like my Scottish accent as she responds first time, unless I’m drunk.