As indicated by Ecnerwal the picture you show is an old style telephone line hookup. When you go looking around for your doorbell transformer it may look like one of these:
Mounted on cover of an electrical junction box similar to the following. Liable to be found in garage or basement fairly close in distance to the bell button and bell unit.
Nope. That's a phone line terminal block. Old school. May have rudimentary surge supression built in. The heavy black wire is drop cable (from the pole to your house)
It's not your doorbell transformer.
Did you put fresh batteries in the Nest? No. Because the Nest doesn't take batteries :)
So that raises a question. How does Nest power itself? It has a lithium battery (like a phone) but that has to be replenished somehow.
The answer is, Nest depends on the fact that thermostat wiring is in series with the furnace relay. Power flows
I would adjust the dampers so the ones in the smaller rooms are not fully open this will put more flow to the larger room. Things to think about that can reduce flow to a room is the bottom of the door jamb tight to the carpet or floor this can act like a damper once the room is pressurized the flow will be reduced with the damper open. If this is the case ...
Which Nest Protect should I get?
Just check the smoke alarm you have now. If it connects to [line voltage] wires, you’ll want Nest Protect (Wired 120V). If it doesn’t, you should get Nest Protect (Battery).
Those colored wires in your ceiling look like 24 gauge thermostat wires, unsuitable for line voltage. I surmise your old smoke directors ran on 24 volts....
Since you have a R841C (with an integral transformer)
You have your terminals on the relay confused. Connect RH to the HOT terminal from the relay and W1 to to the NEUTRAL terminal from the relay. C on the Nest is left unconnected, and you do not need a separate transformer here.
If this was an R841D (standalone relay)
You have your terminals on the Nest ...
With only two wires between the thermostat and the boiler, you're not going to be able to power the thermostat, and call for heat. You'll need at least three wires for that.
The C terminal on the controller is likely the COM terminal, though I can't say for sure. According to the schematic, pin 2 of the PCB connector is C. But I'm not sure where it's ...
Bit of Nest history
Nest often has a sub base issue. Usually the issue is contained to the cooling side. Rh is power input for the heating side. So that wouldn't be my first guess.
Remove Rh and G and connect them together with a wire nut or simply twisting together. It doesn't have to be a very good connection, it just has to be a connection. This ...
I fixed it myself. In the manual (page 18) there is the following image.
As shown on the photo in the question:
From left to right:
The red "bridge cable" is meant to close the circuit in order for the next two (bus +/-) to work. But the bus connectors only work with with an eBus system. Which is not compatible with the Nest Heatlink.
The two wires that ...
A true zone system allows different areas of the house to be isolated, by closing off certain areas using dampers, or just having completely isolated air handlers.
This allows fairly accurate control of the temperature each zone, allowing a specific (and if desired, different) temperature to be maintained in each.
The Ecobee ...
I ended up finding the problem - the black (Rc) and red (R) wires going to my thermostat were joined together in a junction box between the furnace and the thermostat (why I don't know).
I've now separated the black from the red, and installed the new thermostat with black as 'C' and red as 'Rh'. It's working great!.
Thanks to @chris and @ThreePhaseEei for ...
The guidance we are/have been providing in the comments.
The direct answer, is that you have a current carrying wire directly tied the return. (E.g., Neutral & Live In wired together). While this may not be exactly what happened, its an example.
Unfortunately, the diagram the book shows you is possibly misleading and therefore it is likely you were ...
The object in the photos is a 230V "immersion-heater timer". Most traditional UK heating systems have a "programmer" instead but I guess you could have an installation that just uses the timer. I'm assuming IE practices are similar to the UK.
In that case, wire 1 on the old timer would have provided switched-live to a 230V thermostat and the 230V thermostat ...
According to the wiring diagram I found, typical wiring is as follows.
1 END SWITCH (To circulator or another valve)
2 END SWITCH (To circulator or another valve)
3 TH/TR (Thermostat and Transformer)
4 TH (Thermostat)
5 TR (Transformer)
You'll have to verify this is how your valve is wired, but it looks just like the diagram to me. If this is how it's ...
If you have forced air A/C and radiant heat, you almost certainly have two separate transformers. So you'll have to use a thermostat that can work with separate transformers.
If the thermostat you choose requires a C wire, you'll likely want to supply the C from the A/C transformer. It's almost always easier to get the C wire from a forced air system, than ...
Nest customer service is probably your best bet, but I'm going to give you a guess.
In a two wire install the Nest charges itself when the boiler is off, using the difference in voltage between the two sides of the on/off relay inside the Nest itself. A small amount of current is allowed to flow through the charging circuit, and back to the power supply ...
The voltage drop I saw was due to the triggering of the low water cut off system. When the LWCO kicked on it dropped power to the thermostat. Thank you for the tip @ThreePhaseEel !
Gotta get some of those leaky radiators fixed.
As a side-note, the Ecobee handles the power drop better than the Nest. I tried two different Nest-E units and they both read 5-6 ...
The Honeywell device does not provide a C wire out. There is fairly open access to it; perhaps you can pull a rabbit out of a hat.
Otherwise add a second transformer (2 wires from this new transformer). Phase it correctly, I discuss how to do that here.
The wire currently hooked to Y and C will be going off to your air conditioner condenser unit. Y is cooling.
C is common, and yes, you can connect another wire to that terminal.
You appear to have a two-stage furnace however, with W1 and W2. That means you have a couple options:
1 - Install another wire
To take full advantage of two-stage, you need to ...
In my experience with the Gen 2 it will not. That would be a bit heavy-handed and folks would not be happy to have their AC compressor come on with the winter cover still in place, for example.
It may go into Eco, however, if you're away.
More on that
Yes, you can use the blue wire the way you have described.
Instead of all of that work to attach an extension to the blue wire, I would just cut back some of the brown sheath. That's assuming that there is enough slack in the cable for that to work.
Page 17 of the manual linked in the question has the information you need to wire up remote thermostats, that is, to connect wall thermostats rather than using the control panel on the unit. You will have to run five, six, or seven conductor thermostat cable (depending on the unit) from each unit to its thermostat.
You could follow those instructions to ...
On dual transformer systems, Nest expects the common wire to come from the cool side (Nest Pro Guide, bottom of page 20); look towards your A/C not your boiler.
If there is a common terminal on your A/C control board and
18/5 wire bundle - use one of the extra wires to connect the common terminal to your Nest
18/3 wire bundle
Use Venstar Add-A-Wire (or ...
As you can see mine shows replace by April 2026 although I didn’t buy them until end of Aug 2018 and fitted them a couple of months later. I’d better start saving up for the next ones now!
So i didn’t get the full product at a discounted price, simply received a reduced lifetime at a higher prorata cost :(
Can’t tell you about the end of life nagging but i ...
I'm concerned about @ThreePhaseEel's comment on how the Nest will respond to the switching 24VDC that the diode bridge will provide. Although I'm confident that would be an appropriate location to pull a common wire from, I'm going to construct my own circuit from more standard parts.