Nest 3rd gen boiler wiring

[laverda750]

Hi,
sorry if this has been posted before , I did try to do a search first. but couldn't find anything. My question is where do the PL and SL connect to on the nest if the system was to be rewired? I have a british gas 330 boiler and control panel downstairs and would like to put heat link into airing cupboard with the pump.

Thanks

 

[stem]

You don't give much to go on there, but I seem to remember your boiler is a 'Heat Only Boiler' (ie not a combi) so will have a hot water cylinder attached. In which case none of the boiler wiring [including: PL Pump Live, and SL Switched Live] will change. The wires presently connected to the programmer are the ones that are re-routed to the Heat link. And any existing room thermostat would need to be decommissioned, by removing it and adding a link to complete the circuit.

If you can provide some additional information about your system [The existing controls you wish to replace, and if you have a hot water cylinder and motorised valves on your system] then a more definitive answer can be provided.

 

[laverda750]

Sorry about that. I have british gas 330 boiler and control panel in utility room downstairs,with the fused spur there. I would like to fit the nest heat link in the airing cupboard. where pump ,cylinder and junction box are. What I would like to do is disconnect programmer in utility room, use those wires to connect to the spur and power boiler and take power to airing cupboard. Wire heat link in airing cupboard, decommission thermostat at junction box and use thermostat wiring to power nest thermostat from the 12v out of heat link I have a y plan system. Currently from what I can see the switch live goes to the orange on the mid port and the live goes from the boiler straight to the pump. I will try and sketch it out later if that helps.

 

[stem]

OK then as you have a 3-Port valve you have a ''Y-Plan'

The wires that go from your junction box (Wiring Centre) to the existing programmer (shown as time control in the diagram above and below) are either re-routed to the Nest Heat Link, or if that's not practical then the existing cables / wires are removed and replaced with new cables / wires that go to the Heat Link instead. You still haven't given details of your existing programmer so I can't advise further re the actual connections. But here's the concept:

If you have an existing room thermostat then that should be disconnected and a link inserted between the two terminals where the room thermostats live wires have just been moved from. Again as you don't give details of the make / model of any room thermostat further details can't be given but it will be generally as per the concept below.

 

[laverda750]

It’s says British Gas on the front of the controller but invensys on the back. And a flomasta thermostat

 

[stem]

BG normally put the model number on the front of the programmer, the most common being UP2.

Is the Flomaster thermostat the wired or wireless model?

 

[laverda750]

Yes it’s a up2 and a wired flomasta thermostat (3 wires)

 

[stem]

The wires that now go to the UP2 would go to the Nest Heat link terminals that have exactly the same function:

UP2 N = Nest N
UP2 L = Nest L
UP2 1 Hot Water Off = Nest 4 Hot Water Satisfied.
UP2 3 Hot Water On = Nest 6 Hot Water Call for Heat
UP2 4 Heating On = Nest 3 Heating Call for Heat

Nest terminal L and the two common terminals 2 and 5 should be connected together.

For the Flowmaster thermostat, then it will be as per my earlier diagram. Disconnect all of the 3 wires going to it from the wiring centre and then insert a link to join together the two terminals that the two live wires that went to the thermostat have just been removed from.

 

[laverda750]

thank you. you have confirmed what i was thinking on wiring and about the pl and sl wires