Has anyone successfully installed Nest hotwater function to 30cdi classic boiler?

21 Sep 2020
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United Kingdom
Hi all

A new member here!

I have bought a 3rd generation nest that I want to integrate with my Worcester greenstar 30dci classic boiler. The central heating control is straight forward enough but I can't find much advice on the hot water function wiring on my particular configuration.

The boiler has the optional Worcester bosch diverter valve built in. The control panel is on the front of the boiler. There is no external junction box to tinker with, it's all internal.

Has anyone got the same set-up and have you successfully added Nest to it? Just a 'yes' or 'never going to happen' would be a help at this early stage.

Thanks in advance
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what HW do you have ? is it a vented or unvented cylinder, does it have a control thermostat ? do you have an S plan or Y plan system ? so many variations
Thank you for your responses, I have attached some images that I already have (can add more later).

I believe it is a Y-plan arrangement, with pressurised central heating and vented hot water cylinder.
There isn't a stat on the storage cylinder so the terminations on the control pcb are linked out, however there is a temperature sensor on the cylinder which comes as part of the diverter valve kit.


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Remove the link and wire Nest terminals 5 & 6 across it. Don't link L or 2 to 5.

You shouldn't have the casing off your boiler unless you're Gas Safe Registered - it forms the safety room seal and should only be removed and refitted by a GSR Engineer
Thank you muggles, and duly noted, I just wanted to see if I had a diverter valve in there or not before seeking advice on what was possible.

I now understand why the nest wouldn't need L linked to 5, so to be clear the nest would not want the link between L and 2 for the central heating function also?

Thanks again
Sorry muggles but what link wire ? what are you connecting to 5 and 6 ? the wb diverter valve is completly controlled internally by the pcb and a cylinder sensor so how you getting round this ?
The CDi System boiler has two switch Line connections - one for central heating, and a second for hot water when using the priority hot water diverter kit to allow timing of the cylinder heating. I think there's a factory-fitted link in the DHW terminal, and that's the link the OP is referring to. Could be wrong though, it's about 6 years since I last fitted one
I've highlighted the link across the terminals that a cylinder stat would go to.

So if I understand it correctly, the digital programmer on the front of the boiler should stay active and be set to constant. The Nest is connected as an external thermostat for the central heating and as a dummy thermostat for the hot water, telling the boiler when to fire. So if you program the nest the times you want hot water it just completes the circuit across 5 & 6 at those times duping the boiler into thinking it's not up to temperature. The temperature existing cylinder temperature sensor does the rest as normal. Is that correct?


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Your not duping the boiler your just using the nest how its supposed to work, you connect 5 on the nest to one side of the volt free cylinder stat , then connect the other cylinder stat wire to 7 on the boiler and then 9 to 6 on the nest, your simply putting the nest and the cylinder stat in series.

This is all good stuff!
I don’t have a cylinder stat, only the temperature sensor that came with the diverter kit. The cutting from the boiler instructions advises not to use both. Can I still connect the nest into the stat terminals or tap into the sensor wires located elsewhere on the board?
No you need a stat if you want to use the nest, if you connect the sensor the boiler will control the cylinder temp .
Thanks, so fit a stat and disconnect the sensor?
If so and the nest is integrated, am I right in was I said in my earlier post in leaving the existing programmer connected and active, just set to constant and let the nest give the signal when to heat and when to stop?
If you have connected the sensor you will have to do a factory reset when you connect the stat and yes to leaving the existing programmer on constant.

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