Those images definitely help (and its not as bad as your comments implied; looks a relatively tidy installation compared to some!):
1. One white lead from the Oil Central Heating Boiler
I can't see for sure, but its maybe got more than three cores. If so, its probably permanent live, neutral and earth, then a switched live which is energised when you want the boiler to heat. (I've got a gas boiler, but I can't imagine oil boilers are much different). If its only three cores, then most likely you just apply mains when you want heat. Some boilers also control the pump, so that it can be left running for a short time after the heat turns off - prevents hot spots in the boiler.
2. One white lead from the Water Cylinder (Named Indirect Thermal Control)
This will be a simple mechanical thermostat, which closes the hot water valve when the tank water is up to temperature
3. One white lead from a redish/brown device - which I believe is the pump
Yes, its the pump - see comment in next section.
4. Two black lead from into two separate silver metal boxes - see image below
These are the two valves which control the water circulating to the tank and the heating; you apply a live to open the valve, and they're spring loaded so close when power goes. This is why you've probably got a bypass loop (controlled by the black knob to the right of the immersion heater on the tank, I think, although some of the pipework to it looks a bit odd), so that water can still circulate even if both valves are closed - the knob is on a valve which opens if the pressure builds up in the water circuit.
These valves also have a wire which becomes live when the valve is physically open; its this wire which is connected to the boiler and pump - a very simple way to ensure that the boiler only turns on when you actually want heat. The corresponding wires from the two valves are connected together, so the boiler turns on regardless of which valve(s) are open.
hunty1980 wrote: ↑
Sat Dec 09, 2017 10:13 am
How would I safely trace this wire to ensure the other end is the loose wire behind the programmer in the utility room?
Lots of ways, dependent on what test kit you've got. Here's one which relies on virtually nothing.
1. Turn off power to the heating circuit.
2. With both yellow ends 'floating', measure continuity between one end of the wire and earth (ideally with a multimeter; even a battery and bulb will do). There should be no continuity.
3. Connect one end of the yellow wire to earth.
4. At the other end of the yellow wire, measure continuity between the wire and earth. This time you should get an indication of continuity (probably a resistance of a few ohms at most if you're using a multimeter).
5. Restore the status quo.
You might want to replace that junction box with something bigger, to give you more wiring room; maybe something like this
, although almost any proper electrical box with a terminal block inside will do. If possible, get something that caters for multiple connections for neutral and earth, so that you're not trying to get lots of wires into a single terminal.
Looking at the junction box, I would say that:
1. The wire coming in top left hand corner at the back is the thermostat
2. The wires coming in through the top conduit are probably the programmer
3. The grey wire bottom right is the incoming mains
4. The two black wires out of the bottom are the valves
5. One white wire out of the bottom will be the pump - this is always a 3-core
6. Another white wire is the tank thermostat - 3 cores is usually sufficient
7. The other white wire is the boiler - may be between 3 and 5 cores.
Obviously you'll need to check this very carefully, and trace the connections, before you do anything!
I'd say this is definitely the optimum place to connect your Pi into the system