Smart thermostat install

[KevinJackson]

Hi all.

Have been reading lots, but unsure if my exact ask is covered.

I have a Honeywell ST9100C programmer, located next to a Honeywell thermostat like this in our dining room. This is the only thermostat/programmer for the house.

The programmer is used to turn the Bosch Worcester 27CDi Combi boiler On and Off, as well as programming of course.

The thermostat we just adjust temperature to call for heat or not, when the programmer is On.

Can I just replace the Honeywell thermostat only with a smart thermostat, keeping the Honeywell programmer in place and kept On, so that the smart thermostat then becomes the method to turn On/Off via the thermostat screen or remotely using the smart features?

Looking at something like this Hive type or this cheaper type.

I wonder what sort of wiring I would need to adjust. I can get a picture tomorrow of the current Honeywell wiring when at home.

Any advise or ideas would be most welcome.

Thanks all.

 

[RandomGrinch]

Can I just replace the Honeywell thermostat only with a smart thermostat, keeping the Honeywell programmer in place and kept On, so that the smart thermostat then becomes the method to turn On/Off via the thermostat screen or remotely using the smart features?

You could, but smart thermostats also include scheduling; your programmer becomes redundant.
As your existing stat is right next to the programmer, it wouldn't be too much hassle to rewire them both at the same time.
If you are comfortable to, and with the power safely isolated, remove the covers of the ST9100c and stat and post a picture of the wiring. Hopefully we can advise further!

 

[KevinJackson]

Appreciated RandomGrinch, the existing Honeywell programmer would absolutely be redundant and this is fine.

The problem is, the programmer would have to stay in situ, as it is very 'on display' in our dining room, so removing is not really an option without a big wall patch up, so leaving it On and connected is ok for me, rather than rewiring everything and it being off/blank.

If we left the Honeywell programmer in situ and left on, I guess the smart thermostat could take care of the programming and on/off, plus temp adjustment, almost treating the existing Honeywell programmer as a through port for power?

Will turn power off and post pictures.

Cheers

 

[ericmark]

Yes the WPB version would work, however the only advantage is the phone control, it will not heat the home any better than the old system, and as to only replacing the thermostat, depends on if there is a neutral to old thermostat.

Control depends on the home and life style. In the main we have more than one key room, for example my house living room, and wife's bedroom, hers is the naturally coldest room in the house, but only want it heated over night, but Living room don't want heating over night, but does want heat during the day, so the programmable head on the TRV in her room set to run over night, and living room TRV heads set to run during the day.

But clearly the TRV's will only work if the boiler is running. So the options.
1) Wall thermostat in the hall, and hope it runs boiler when other rooms need heat.
2) Wall thermostats in living room and bedroom, wired in parallel.
3) Use linked TRV heads, so the TRV's can make boiler run.
There are other options of course, but to improve on existing system, your really looking for a thermostat/hub which will allow selected TRV heads to link to it, in my case dinning room, kitchen, office, craft room and my bedroom are used at same time as either wife's bedroom or living room, so a simple un-linked programmable TRV head is good enough for those rooms. And the programmable bluetooth heads cost me just £15 each in 2019, but to get a linked system looking at.
Honeywell evohome
Hive
Drayton Wiser
Tado
Not Nest, and Hive can't work with OpenTherm, although not convinced OpenTherm helps. The other improvement can be geofencing, I have tried the Nest, and it was a bit of a failure, Wiser uses IFTTT, not sure about the rest.

So yes the thermostat you have linked to is cheap at £40, but will it improve the system?

I have found run time is important, a thermostat may have a droop of 0.5ºC to 2ºC (difference between on and off temperature) and at first glance 0.5ºC seems best, however one that means boiler is being switched on/off more often, so it can't modulate to reduce energy use, and also some radiators in the home may not have time to get hot, I see complaints about radiators only hot at the top, where boiler has switched off before the radiator has had chance to get warm.

I made an expensive mistake, I installed Nest Gen 3, I thought it would work with Energenie TRV heads, and if does not, spending £40 is better than £90 if the system works, but spending £40 and latter spending another £90 because the system does not work is clearly not what you want, so will a single thermostat work for you?

 

[KevinJackson]

Thank you ericmark, that is great info, cheers.

The only reason for the smart thermostat, is for having remote control via smart app on on/off and temperature control, whether sitting in bed or away and coming home to warm house etc.

I will check whether neutral present etc tomorrow when I can take pictures.

We have a simple setup. No TRV's and the whole house is on or off, with same radiator settings throughout. Single thermostat.

Only wish to replace Honeywell thermostat with a smart one to bring these above features, cheers

 

[KevinJackson]

Turns out, I already had a photo of the current Honeywell thermostat already:

Looks like, live, neutral and earth?

I found this smart thermostat which looks to have good reviews on Amazon.

I read talk of bridging COM & live, how would I know if I need to do this?

Cheers

 

[RandomGrinch]

Looks like, live, neutral and earth?

Afraid not, its a Live, a switched Live (in blue) and an earth connection.
We would need to see behind the ST9100C.

Just to note, if you were to remove this stat, the wall doesn't look like it would need much patching up.
A new stat would cover up most of the space taken by the ST9100C - you may be surprised how little work needs doing to tidy up the walls.

The Meross would be ok, but look out for other Black Friday deals.
I think Hive is on offer on Amazon at the moment.

 

[KevinJackson]

Oh no....

If I did not remove the ST9100C, could I grab the neutral from there, or am I well off?

i.e. split the neutral, so it goes to ST9100C and thermostat? thanks

 

[KevinJackson]

Just found this, looks like a Tado smart thermostat which does not need a Neutral?

https://www.amazon.co.uk/dp/B07FZ3P393/ref=cm_sw_r_cp_api_glt_fabc_8FV1THF883WEKN6Y34G1?_encoding=UTF8&th=1

I found a thread where someone had the same Honeywell original thermostat, with Live, Switched Live and Earth, which looks the same as me?

https://community.screwfix.com/threads/what-wall-thermostat-without-neutral.245493/

Would this be suitable? thank you

 

[RandomGrinch]

Would this be suitable? thank you

Yes, a wired Tado is battery powered and would be a straightforward swap for your two wired stat.

Although providing a Neutral connection to a mains powered stat, may still be a simple option, depending on what's behind the ST9100c.