Wiring Google Nest 3rd Gen Heatlink to Worcester Greenstar Highflow 440 Standalone Boiler

Hi folks,

I'd like to get my Nest thermostat up and running with the gas combi boiler (Worcester Greenstar HIghflow 440 Standalone). FYI - I have tried to get this installed by a professional, but I've been let down 3 times now. 5 of 6 quote requests on the Nest website didn't even bother replying either. I've been told by numerous folk now that it's straightforward enough and should only take 10 minutes to wire. I'd still like to do it properly though!

Below is a photo of the boiler wiring currrently. You can just see the control panel on the right which is the current thermostat. I assume I can just disconnect this from the board when the Nest is installed as there will be no use for it.

Page 27 of the manual shows the different layouts. I believe option 10 should accomplish what I need. We usually leave the hot water feed on constantly and still being gas noobs (we always used oil), we're still not sure if this is the most efficient method of a gas combi boiler.

1) The existing L and N wiring in ST4 connects to an isolator switch just above the unit, but is tracked through the wall. Can I just leave this in place and also connect the Nest Heatlink to these L and N feeds?

2) I have some 5-core flex cable. Would this be sufficient to connect everything I need to the Heatlink with a single flex cable?

3) I assume ST8 in the photo is the wiring that goes to the thermostat control panel? This would be unplugged and routed to the Nest Heatlink. We don't need a separate thermostat control as we'll just be using the Nest plugged in via mico-USB.

4) Would option 10 on the wiring diagram be sufficient for this? Really appreciate your opinions. Thank you!

The ST4 terminal block is where the supply to your nest should come from. The LR terminal is your switch return live from the nest to control the central heating. The ST8 terminal block is where your switch return live from the nest to control the hot water appears to go. Not really familiar with this model of boiler, but that’s how I am reading it.

diditrain said:

The ST4 terminal block is where the supply to your nest should come from. The LR terminal is your switch return live from the nest to control the central heating. The ST8 terminal block is where your switch return live from the nest to control the hot water appears to go. Not really familiar with this model of boiler, but that’s how I am reading it.

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Thank you for that. Sorry for the delay! I've got the wiring all done on the Nest side, but haven't connected anything up yet. I'm just not sure how the hot water works on this boiler. If it is just connected to the control panel and I can manually turn off/on then I am ok with that, as it will just be left on anyway. I'm not sure if it actually works this way.

I didn't think of looping L to 2 on the Heatlink which is what everyone else seems to do.

I will redo the L wiring as I found it really fiddly poking 2 connections in, but that's how it looks on the Nest side, connection-wise.

The boiler already has a separate live feed, so I'm just going to leave that in place and do the following from the Heatlink:

Nest Boiler
N > Ns
L > Ls
3 > Lr
E > E
Note: The boiler has a separate L and N feed which runs to a 3A isolator.

From what I remember regarding the boiler, I believe it functions like a combi, but it also gives you the ability to control the inbuilt hot water storage vessel via your controller if you want to. If you don’t make any electrical connections to ST8 for the hot water control, then you still get your hot water on demand.

diditrain said:

From what I remember regarding the boiler, I believe it functions like a combi, but it also gives you the ability to control the inbuilt hot water storage vessel via your controller if you want to. If you don’t make any electrical connections to ST8 for the hot water control, then you still get your hot water on demand.

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Thanks! I'll just leave the ST8 terminal block, go with the other connections and see what happens.

Don’t forget your brown sleeving on your switched live.

All installed and I think that's it sorted! I left the timer/control panel connected first of all as I'm not sure exactly how that interacts with the Nest. I've left both CH and DHW turned on from the control panel however, I am still able to control the cental heating from the Nest. When turning off, the boiler stops firing. It will fire when hot water is used which is exactly what I need.

I'm not totally confident that it is switching on/off properly. I've set the scheduled timer from the Nest app and will just closely monitor how it operates.

I think if I unplugged the timer, it may mess with the always on hot water. I can't figure out how it would still work but if the schedule doesn't work as expected, that will be my next course of action.

Thanks @diditrain for your help with this!

leccylen said:

All installed and I think that's it sorted! I left the timer/control panel connected first of all as I'm not sure exactly how that interacts with the Nest. I've left both CH and DHW turned on from the control panel however, I am still able to control the cental heating from the Nest. When turning off, the boiler stops firing. It will fire when hot water is used which is exactly what I need.

I'm not totally confident that it is switching on/off properly. I've set the scheduled timer from the Nest app and will just closely monitor how it operates.

I think if I unplugged the timer, it may mess with the always on hot water. I can't figure out how it would still work but if the schedule doesn't work as expected, that will be my next course of action.

Thanks @diditrain for your help with this!

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For the hot water side of things, when there is no longer a demand for hot water, the boiler will continue to operate until it has replenished the heat bank. The nest should now have full control of your heating system with your original integral control set to the constantly on position.

Update: Everything appears to be working perfectly!

When I first enabled the schedule on the unit, it came on earlier then expected. I then decided to schedule it to come on for the following morning at 7am, and that it was probably something I did wrong. It was certainly turning off ok.

Come 7am the next morning, we are all more or less sweating buckets. The house is absolutely roasting. It was only then I totally forgot about the pre-heating opton being enabled. I don't understand the point of this if it's going to switch the heat on up to 5 hourse before you asked it to. Presumably it assumed your target temp is to be reached at 7am but either way, it isn't very clear during the setup process. It's been like 6 years since I last disabled these options in my last house, so I totally forgot about them. I have disabled Auto-schedule, True Radiant and Sunblock. It looks like the app interface hasn't been updated in all these years, nor is there a dark mode, but these are just minor grumbles.

Like you said, I have both CH and DHW constantly on from the control panel. This still enables me to turn on/off the heat with the Nest, and set schedules etc, so I am just going to leave the littel timer connected. It won't do anything anyway.

One thing I'm curious of is the hot water. Is it more efficient to leave it on constantly so that hot water is replensihed or is it better to scheduled the hot water? I'm guessing scheduling would be a bit silly given the limited hot water capacity.

Thanks!

leccylen said:

I don't understand the point of this if it's going to switch the heat on up to 5 hourse before you asked it to.

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The point is that you set up a schedule of what temperature you want at what time and the nest brings the heating on at the right time to achieve that. The nest will vary the time that it brings the heating on based on the actual temperature of the room, you can limit how many hours earlier it will come on if you wish.

leccylen said:

Presumably it assumed your target temp is to be reached at 7am but either way, it isn't very clear during the setup process. It's been like 6 years since I last disabled these options in my last house, so I totally forgot about them. I have disabled Auto-schedule, True Radiant and Sunblock.

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Why would you disable all the features that make the thermostat smart? Isn't the whole point of installing one to have smart control and reduce energy bills?