ST9100C and CM907 conversion to smart heating advice needed please

[lostboi]

Hello,

I am a complete novice with this topic. Apologies.
I realise there are some other threads on this same question, but my individual setup seems weird. Like I don't understand how the receiver to replace the ST9100C would/could work due to the lack of wires.

I currently have:
A downstairs thermostat wired into the wall, a Honeywell CM907 (photo attached).
An upstairs thermostat wired into the wall, another Honeywell CM907.
A boiler in my downstairs utility room.
A panel underneath the boiler, a Honeywell ST9100C. (Photo attached of both the backplate wiring and the wiring behind the plate. I note there seems to be an unused brown wire, not sure what this is?).
A hot water cylinder (immersion heater?) upstairs in a cupboard.
In the same cupboard, a big box on the wall full of wires (photo attached).

There seem to be 3 metal box valves in the cupboard upstairs.
I believe the two wired CM907 panels control the two separate heating zones via these valves, and the third must have something to do with the hot water?

I would like to swap this kit for smart heating/hot water. Any suggestions on how to achieve this?
The challenges as I see it are that I have two separate zones and would like to keep it that way (HIVE say I need two receivers and two thermostats for this?), and the ST9100C panel underneath the boiler which is usually where you install the smart 'receiver' may only have wires for the hot water, so the smart system wouldn't work?

If the heating + hot water approach is too difficult, is there a way to do smart heating only?
Any advice greatly appreciated.

Thanks.

 

[muggles]

Easy enough to do. I'd recommend two Nests. Heat Links can be wired directly into your wiring centre (last pic) and the wires supplying the existing CM907s repurposed to provide power to the Nest thermostats. The 9100C wires can be made safe and put behind a blanking plate

 

[ericmark]

What do you see as "Smart"?
1) Adjusting heating start times to the internet weather report.
2) Goefencing.
3) Geofencing combined with occupancy detection.
4) Open window detection using PIR.
5) Open window detection using temperature drop.
6) Telemetry (can use a phone to adjust a) from inside the room, b) anywhere in the world.
7) Adjusting radiator temperature rather than on/off to reduce hysteresis.
8) Using a mark/space ratio to reduce hysteresis.
9) Calculating and remembering how long it takes to heat a room to speed up re-heat times without over shooting.
The list goes on, and no single system will do it all, and the re-heat time of a room or house and standard times to get home, will alter which system will work best for you. My house top floor I have two bedrooms, a bathroom, an office, and a craft room, the office and craft room as used during the day, so grouping them on same zone as bedrooms is daft, we eat breakfast in the living room, and only the evening meal is eaten in the dinning room, so dinning room only heated 4 to 8 pm.

I have main house and flat on their own zones valves, as flat is rarely used, but my house has oil central heating which does not modulate, with a modulating boiler the only wall thermostats which can work with OpenTherm and work as master/slave seem to be the EPH, and since designed to work that way, they don't link to TRV heads. Nest wall thermostat claims to work out what time it needs to start heating so ready at set time, Drayton TRV heads also claim to do the same, Nest does not link to TRV heads, where Hive does, but Nest algorithms are far better to Hive, and Hive does not have OpenTherm. The list goes on, EvoHome, Tado each has good and bad points, there is no best, just which one suits your house and boiler.

With oil turning boiler off/on does not really matter, with a gas modulating boiler if it turns its self on/off OK but if a wall thermostat turns it off/on it can make it inefficient, where the boilers software makes it restart flat out, rather than modulated when switched off/on by an external thermostat. So with gas we look for many makes at OpenTherm where the boiler is turned up and down instead of on/off, but some makes have not signed up to opentherm, so your very limited as to what thermostat will work efficiently. With some the wall thermostat controls boiler output, and others all it there for is to stop the boiler cycling when we get a warm spell.

However most gas boilers monitor the return water temperature and can use that to set how much to modulate (turn down) the output, so with most systems the TRV head is king, and if the TRV is programmable there is very little need for motorised valves, so you have to work out the final goal. So if only buying the wall thermostat Nest is far better than Hive, but if also buying programmable TRV heads, then Hive better than Nest.

Other than EPH I don't know of any other make where you can have two or more wall thermostats working opentherm, others may know different, but if you want a modulating thermostat with zone valves, seems must be EPH, Drayton do a programmer designed for three zones, two heating and one domestic hot water, but using simple on/off control.

So life style, boiler make and type, design of house, where the sun shines, all affect which central heating system is best, EvoHome is likely the oldest offering multi-zone control room by room, and still likely one of the best, however it also comes down to other automated controls, it seems I can use my Energenie TRV heads to work my Energenie sockets and so turn on the air conditioner unit when required, never set it up to do that, I switch it no manually with phone.

As to Nest Mini, they are like naughty boys, and I have stopped using them to switch on lights, as they would switch them off when asking it to stop playing music, also with 5 light switches had a problem with them seeming to have a mind of their own, but removed two and other three now work great, maybe my Nest Mini does not like my lack of teeth when a give a command?

But I have been reducing the automation in my house, finding simple timers work better. So I have 4 x Energenie TRV heads, 5 x eQ-3 TRV heads, 5 standard TRV heads, bathroom works with DHW, and Nest Gen 3 for main house, and simply bi-metal for flat under house, and flat and house independently controlled with two pumps and two motorised valves, flat very rarely heated, using gravity DHW and oil boiler. Although the Energenie heads can have geofencing set up I don't use it, I only use geofencing on the Nest, and best value for money must be the bluetooth eQ-3 TRV heads at £15 each.

 

[stem]

Often it's simply a matter of replacing individual components with smart devices. The design of your system currently presents some difficulties for a novice. To start with you currently have 3 devices at different locations; 2 CM907 room thermostats, and a ST9100C timer for heating the hot water cylinder.

To go fully smart would normally involve re-routing the wiring from one of the room thermostats and the water timer together at the same point. [Nest, Hive, Tado for example] so as @muggles pointed out this rewiring would be done at the wiring centre. ["box full of wires"] However it would require a good working knowledge of how the heating system is presently connected and functions as well as a good understanding of electrical circuits. Do you know how to find out for example where each of the wires in the wiring centre goes and what it actually does?

The next problem is the CM907 room thermostats are battery operated so do not have a 230V supply connected to it. With most smart stats either the receivers (the device where the thermostat wiring goes eg Nest, Hive) or the thermostats themselves are mains powered so a new 230V supply will need to be installed for them.

As I see it, the easiest route to go 'smart' would be to leave the hot water controlled by the ST9100C timer as it is now, and install two battery operated smart thermostats to replace the existing battery operated room thermostats. Tado make a wired smart thermostat with a two wire connection.

Another alternative would be Google Nest-e The two wires at the existing room thermostats would each connect to a battery operated Heat link. The downside here is that the Heat link and Thermostat are two separate devices so unless you wanted to move the existing thermostat wiring somewhere out of the way, both would be out on display.

Finally if you wanted to use a mains powered thermostat instead, one of the existing thermostat wires (most likely the brown wire in the 'A' terminal) will already be a 'live', and there appears to be an unused grey wire that already goes to the wiring centre. If so, that could be connected to a neutral to provide 230V power to a thermostat.

Regarding keeping the two heating zones, if your house is a fairly new build, the building regulations will have dictated that it be installed this way, so it should remain with two thermostats.

 

[ericmark]

As usual @stem is spot on, as to

Regarding keeping the two heating zones, if your house is a fairly new build, the building regulations will have dictated that it be installed this way, so it should remain with two thermostats.

reading government guide lines it seems rather ambiguous as to what is considered as a zone, some councils consider the TRV as forming a zone, there is no black and white.

I would say winter is not the time to play with central heating wiring, I would suggest swap some of the existing TRV heads for electronic types, then no wiring involved, maybe select the thermostat you like, and get TRV heads which will work with it, but I bought 5 cheap (£15 each) electronic eQ-3 bluetooth TRV heads and it has transformed the heating system, I would do down stairs first with the really cheap TRV heads, without bluetooth seen the eQ-3 at under £10 the Terrier i30 very similar, if they do what you want buy more of same for upstairs, if not move the cheap ones upstairs and buy more expensive for down stairs.

Keep it simple, try screw on methods first with no wiring.

 

[lostboi]

Thanks guys this is all very helpful. I think if I'm honest what this has told me is that I need a professional if I want full smart hot water/heating as modern regulation houses are a little bit picky to install smart hot water/heating.

The exception to this is the tado wired smart thermostat that @stem mentioned. I am tempted to simply replace the two thermostats on the walls with two of these tado thermostats, plug the receiver into my internet router... and leave the hot water controlled by the ST9100C.

My confusion is in the tado description of this wired thermostat product though:
"You need the Wired Smart Thermostat Starter Kit if your home has an existing wired thermostat with a combi boiler (i.e. no hot water tank). If your home has one of the following: A hot water tank and you want to control the hot water via the tado° app. Or, your home has either a thermostat with a wireless connection to the boiler or no thermostat at all, you will need the Wireless Smart Thermostat Starter Kit with Hot Water Control."
That doesn't sound right for my situation because I have a hot water tank and do not have a combi boiler??

 

[stem]

OK, so you do have a hot water cylinder (they call it a tank ) and if you want to control it with Tado, you would need the Wireless Smart Thermostat Starter Kit with Hot Water Control.

On the other hand, if you are happy to leave the hot water control with the ST9100C timer (which means it's not controlled by Tado) you don't need it.

 

[lostboi]

OK, so you do have a hot water cylinder (they call it a tank ) and if you want to control it with Tado, you would need the Wireless Smart Thermostat Starter Kit with Hot Water Control.

On the other hand, if you are happy to leave the hot water control with the ST9100C timer (which means it's not controlled by Tado) you don't need it.

Thanks. Sounds like I am interpreting it badly. Seems combi boiler with no tank and existing wired thermostat = mandatory wired tado but
regular boiler with a tank = wireless is only required if I want to control the hot water as well. In the product info it doesn't actually say what you need if you have regular boiler with a tank but don't mind not controlling the heating.

Anyway, tado wired thermostats starter kit (thermostat plus receiver which plugs into Internet router) and an additional thermostat looks like what I need.. I think

Thanks!

 

[stem]

I think you've got it. A combi boiler only has external controls (thermostat) for central heating. Hot water is produced on demand when a hot tap is opened, so no need for any time controls to heat up a hot water cylinder.

Which as far as Tado would be concerned is what you have. There isn't any hot water cylinder to add to the Tado to control, because it is already being done by the ST9100C.

 

[lostboi]

I think you've got it. A combi boiler only has external controls (thermostat) for central heating. Hot water is produced on demand when a hot tap is opened, so no need for any time controls to heat up a hot water cylinder.

Which as far as Tado would be concerned is what you have. There isn't any hot water cylinder to add to the Tado to control, because it is already being done by the ST9100C.

Just wanted to pop back in and say thanks for the advice. The tado wired thermostats worked a treat and I have left the hot water on the old honeywell. Cheers.