Nest Y-Plan Instructions Incorrect ??

[DIYAd]

Hi all,

So I'm currently planning the install of my Nest 3rd Gen but there's 1 part which has me confused/stumped.

The hot water cylinder thermostat (Honeywell L641A) has 3 terminals; C, 1, and 2. According to their instructions https://heatingcontrols.honeywellhome.com/Documents/Installation-Guide/pdf/1152.pdf the heating load connects via terminal 1. Now it does say "Terminal 2 used on Y-Plan systems" but as i understand it that's used to turn the HW off so no heating load.

My HW thermostat is currently wired as followed;

Terminal C to the Programmer
Terminal 1 to Boiler, Pump and Orange on the 3 way valve
Terminal 2 to Grey on the 3 way valve

However....

The Nest Y-plan instructions show the heating load comes out of terminal 2

Any clarification would be greatly appreciated, thank you.

 

[jackthom]

Go by the Honeywell instructions for their specific thermostat and stick to the way it is currently wired.

The Nest diagram may well apply to other makes of cylinder thermostat but not yours.

 

[Palmbay]

I note Jackthom's reply regarding different cylinder stats, however, I have found that most cylinder stats are internally wired as above. I have tried swapping the 1 & 2 about but I still get no hot water. I thought I was supposed to get a hot water icon on the NEST gen 3 Learning room stat but there is none.

I have drawn what my setup is, damned nuisance! can anyone look at my schematic and see where I have gone wrong. Thanks in advance.

I have since rewired from scratch and found a pinched wire, clamped to the insulation instead of the wire itself. I then found the call for hot water occurred when the tank stat was set to its lowest setting, so ended up swapping 1&2 (see diagram) over.

I couldn't find any electrical schematics specifically for the Y-Plan with NEST installed so drew my own. If anyone wants reassurance, then I can say that apart from the tank stat swap over of wires 1&2, this works perfectly.

The reason no "hot water" icon was showing on the NEST display was because I had chosen the wrong boiler type. By going into advanced settings I changed this to a gas system boiler and it then appeared.

 

[muggles]

If you're not getting a hot water icon on Nest, the issue is with Nest not with your wiring. Have you set it up correctly? Does the hot water work if you press the override button on the Nest receiver?

 

[Palmbay]

Hi Muggles, thanks for your reply. I presently get no hot water when the over ride is pressed. I have seen a reply in a NEST forum on the subject of no HW icon, this might be the problem. When home, I will go back into: settings>equipment>continue>pro setup>continue
to see exactly what boiler is selected. He suggests choosing a "System Boiler" or "Other" and manually changing the HW interface to "On/Off", instead of "Not Connected".
It did flash through this when initially setting up and I recall some issues at the time which involved much running up and down stairs, which is where the heat link is installed, in the airing cupboard. I am surprised I can't access set up from the iphone app. I will report back once back home and checked it out. If not I will rip the spaghetti soup original wiring out and do a proper fit out to be doubly sure. I will upload a couple of pics of what I have inherited!

 

[Palmbay]

Hi all,

So I'm currently planning the install of my Nest 3rd Gen but there's 1 part which has me confused/stumped.

The hot water cylinder thermostat (Honeywell L641A) has 3 terminals; C, 1, and 2. According to their instructions https://heatingcontrols.honeywellhome.com/Documents/Installation-Guide/pdf/1152.pdf the heating load connects via terminal 1. Now it does say "Terminal 2 used on Y-Plan systems" but as i understand it that's used to turn the HW off so no heating load.

My HW thermostat is currently wired as followed;

Terminal C to the Programmer
Terminal 1 to Boiler, Pump and Orange on the 3 way valve
Terminal 2 to Grey on the 3 way valve

However....

The Nest Y-plan instructions show the heating load comes out of terminal 2

Any clarification would be greatly appreciated, thank you.

Have you resolved the issue?

 

[muggles]

Hi Muggles, thanks for your reply. I presently get no hot water when the over ride is pressed. I have seen a reply in a NEST forum on the subject of no HW icon, this might be the problem. When home, I will go back into: settings>equipment>continue>pro setup>continue
to see exactly what boiler is selected. He suggests choosing a "System Boiler" or "Other" and manually changing the HW interface to "On/Off", instead of "Not Connected".
It did flash through this when initially setting up and I recall some issues at the time which involved much running up and down stairs, which is where the heat link is installed, in the airing cupboard. I am surprised I can't access set up from the iphone app. I will report back once back home and checked it out. If not I will rip the spaghetti soup original wiring out and do a proper fit out to be doubly sure. I will upload a couple of pics of what I have inherited!

I'd be rewiring that

 

[stem]

.....including an earth connection to the backbox.

 

[Palmbay]

I definitely will be, but with a Honeywell 10-way junction box. I have recently moved in so lots to do, just need some hot water!

 

[Dan Robinson]

Seen worse

 

[Palmbay]

All now working 100%. After much faffing about ending up total rewire of junction box and setting the NEST to the correct boiler type. See above edits.