We've just bought our first home and it currently has no room thermostat. The heating and hot water is controlled solely by an old Drayton LP112 programmer in the airing cupboard and TRVs on all the radiators (apart from the towel rails in the bathroom and downstairs shower room).
I'd like to install a Nest thermostat and before I fork out £80 to have it installed I wanted to see if it was something I could get my head around and do myself. Much research and learning how my current heating system works, I think I've figured it all out but thought I'd post on here to make sure I've not missed anything.
I managed to track down the following diagram on the Drayton website which helped me identify each terminal and connection:
http://www.draytoncontrols.co.uk/WorkArea/DownloadAsset.aspx?id=28350
What I've figured out:
* I have a Y-Plan system. All the connections terminate in a junction box in the airing cupboard. The connections almost entirely match up with the mid-port valve schematic in the above document.
* I have mains power coming in through an isolator/switch which terminates on the L, N and E terminals (1, 2 and 3).
* The programmer is connected to L, N, E, the common terminals for heating (4) and water (6) and the satisfied terminal for water, 8.
* The mid-position valve and cylinder stat are wired exactly as above.
* The boiler cable has some additional wires and seems to be connected to the boiler pump live via a connecting block - I'm assuming this is because the boiler (Baxi Solo 2 PF) is a pump overrun boiler and controls the pump directly.
* There is a red jumper between terminals 4 and 5 - I assume this connection would normally be made between common and call for heat in the room stat but as there isn't one, a permanent connection is made so whenever the programmer turns the heating on, a call for heat is sent.
Does this all sound good so far?
The Nest wiring diagrams show that the Heat Link needs a permanent L and N (no E) and also has a Common and Call for Heat terminal. It also has two low voltage terminals T1 and T2 that can be used to power the Nest stat itself (lets ignore those for now as I will probably plug the stat in using its USB adaptor).
It appears I have two options for wiring this up:
1. Just like any other room stat in the schematic above. I would need to use 4 core cable to connect the permanent L and N from terminals 1 and 2 in the junction box to L and N in the Heat Link, and link the common and call for heat terminals to terminals 4 and 5 in the junction box. I would then remove the existing jumper between 4 and 5 in the junction box. The programmer would need to be set to leave the heating ON rather than TIMED to enable the Nest to fully control the CH.
2. I can connect L, N and call for heat as above, but connect a small jumper cable between L and C in the Heat Link to permanently enable its heating circuit and thus bypass the programmer for CH completely. The programmer setting would have no effect.
In both cases the programmer would continue to control the hot water.
So:
* Have I figured this out correctly?
* Are the two methods for wiring up the Nest correct?
* Which one should I choose? It seems like the former would allow me to still turn the heating off entirely at the programmer whereas the latter would be simpler and would mean just one device is responsible for CH control.
* If I go with the latter approach, I can re-use the small jumper lead currently in the junction box between 4 and 5 to jumper the L and C terminals in the Heat Link. For the remaining connections, I assume I'd need 3 core and earth? If so, how would I terminate the earth? I can terminate it to the earth terminal in the junction box end but the Heat Link has no earth.
Oh, one more thing: the cylinder stat wiring confused me for a moment - it is connected to terminals 6, 7 and 8 as in the above schematic using blue, brown and green/yellow wires respectively. Has somebody been a bit lazy and just used normal T+E to wire this up and the earth wire is being used for the hot water satisfied link - my understanding is that earth wiring should never be used for anything other than that.
Thanks!
I'd like to install a Nest thermostat and before I fork out £80 to have it installed I wanted to see if it was something I could get my head around and do myself. Much research and learning how my current heating system works, I think I've figured it all out but thought I'd post on here to make sure I've not missed anything.
I managed to track down the following diagram on the Drayton website which helped me identify each terminal and connection:
http://www.draytoncontrols.co.uk/WorkArea/DownloadAsset.aspx?id=28350
What I've figured out:
* I have a Y-Plan system. All the connections terminate in a junction box in the airing cupboard. The connections almost entirely match up with the mid-port valve schematic in the above document.
* I have mains power coming in through an isolator/switch which terminates on the L, N and E terminals (1, 2 and 3).
* The programmer is connected to L, N, E, the common terminals for heating (4) and water (6) and the satisfied terminal for water, 8.
* The mid-position valve and cylinder stat are wired exactly as above.
* The boiler cable has some additional wires and seems to be connected to the boiler pump live via a connecting block - I'm assuming this is because the boiler (Baxi Solo 2 PF) is a pump overrun boiler and controls the pump directly.
* There is a red jumper between terminals 4 and 5 - I assume this connection would normally be made between common and call for heat in the room stat but as there isn't one, a permanent connection is made so whenever the programmer turns the heating on, a call for heat is sent.
Does this all sound good so far?
The Nest wiring diagrams show that the Heat Link needs a permanent L and N (no E) and also has a Common and Call for Heat terminal. It also has two low voltage terminals T1 and T2 that can be used to power the Nest stat itself (lets ignore those for now as I will probably plug the stat in using its USB adaptor).
It appears I have two options for wiring this up:
1. Just like any other room stat in the schematic above. I would need to use 4 core cable to connect the permanent L and N from terminals 1 and 2 in the junction box to L and N in the Heat Link, and link the common and call for heat terminals to terminals 4 and 5 in the junction box. I would then remove the existing jumper between 4 and 5 in the junction box. The programmer would need to be set to leave the heating ON rather than TIMED to enable the Nest to fully control the CH.
2. I can connect L, N and call for heat as above, but connect a small jumper cable between L and C in the Heat Link to permanently enable its heating circuit and thus bypass the programmer for CH completely. The programmer setting would have no effect.
In both cases the programmer would continue to control the hot water.
So:
* Have I figured this out correctly?
* Are the two methods for wiring up the Nest correct?
* Which one should I choose? It seems like the former would allow me to still turn the heating off entirely at the programmer whereas the latter would be simpler and would mean just one device is responsible for CH control.
* If I go with the latter approach, I can re-use the small jumper lead currently in the junction box between 4 and 5 to jumper the L and C terminals in the Heat Link. For the remaining connections, I assume I'd need 3 core and earth? If so, how would I terminate the earth? I can terminate it to the earth terminal in the junction box end but the Heat Link has no earth.
Oh, one more thing: the cylinder stat wiring confused me for a moment - it is connected to terminals 6, 7 and 8 as in the above schematic using blue, brown and green/yellow wires respectively. Has somebody been a bit lazy and just used normal T+E to wire this up and the earth wire is being used for the hot water satisfied link - my understanding is that earth wiring should never be used for anything other than that.
Thanks!
