Can I get a dual channel thermostat with this setup?

[slpn1]

This is the wiring block on my Worcester Greenstar 27ri boiler. I just want to check that a dual channel Nest Heat Link will work with it?

If it's simple to wire up, a nudge in the right direction would also be massively appreciated.

Thanks very much,
Simon

 

[ericmark]

The second channel will not be used, it will just control the central heating. I have Nest Gen 3 and rather disappointed with it. Although told it would link to TRV's it does not.

Worcester Bosch only allow their own ebus thermostats to be used, so can't use the OpenTherm option, so you really want a thermostat which only switches off when all rooms are satisfied, every time an on/off thermostat switches off and on again, the boiler starts again from scratch setting the output to match demand, so is not running as efficiently until it has set how much it needs to modulate, the whole idea is the room temperatures are set with the TRV, as each TRV closes more water is forced though those still open, and then the by-pass valve starts to open allowing hot water direct back to boiler, the boiler uses the return water temperature to set how much it needs to modulate (turn down) so it is able to gain the latent heat from the flue gases. It also means a smooth temperature, with little or no hysteresis.

When the boiler is turning on/off all the time, the TRV can't get the temperature so smooth, my oil boiler can't modulate so turns on/off all the time, so looking at the report from the TRV head we get this as the boiler is switching on/off, with gas it should be smooth.

Most the better thermostat connect to the TRV so the TRV heads tell them what to do, Evohome, Wiser, Hive etc. You need to select TRV heads that work with the wall thermostat for critical rooms, but most rooms can use cheaper options, I used eQ-3 heads at £15 each in 2019 when I got them, also Terrier i30 heads are cheap, the head that gives the report shown is TP-Link (Kasa) and needs a hub.

Also found the geofencing on Nest useless, you can set eco and comfort temperatures but not the distance from home when the heating raises to the higher temperature again. And the learning bit, think it was a mischievous little boy when you see the settings it selected.

 

[RandomGrinch]

Or to answer the actual question, rather than ranting about Nest again

This is the wiring block on my Worcester Greenstar 27ri boiler. I just want to check that a dual channel Nest Heat Link will work with it?

If your boiler heats both central heating and hot water:

You have a 'regular' boiler (hence the RI in the name) - heating and hot water is controlled via valves.
Your Nest, wouldn't connect directly to the boiler; it would connect to a wiring centre, that would operate the valves, which in turn would call for heat from the boiler.

So yes, the Nest will likely work with your boiler, but no, it wouldn't connect directly to that wiring block.

If the boiler only supplies central heating, then yes, the C/H output from the Nest can connect to 'LR' (Live Return) on the boiler.

 

[slpn1]

This is great. Thanks to both of you.

 

[ericmark]

I would have thought Nest would connect here

but normally until connected there is a loop wire, so will assume some where some dip switch needs switching?

 

[ericmark]

I have found this and this in the instructions. Plus this but nothing up to now to say how one selects which system is used, Nest is also designed for all three, but seem to remember the Bosch ebus is not OpenTherm.

In many cases the electrical connections are in a sealed compartment, so only gas safe people can access them, so as an electrician we may change a thermostat but are not involved wiring one in to start with, when I have there has always been a link which needs removing to fit the thermostat, and I can't see one in your picture, and could not find any reference in the manual to them.

 

[slpn1]

Thank you. I found my manual for my wiring centre and it all seems to make sense. Although not shown on photo above (I got that one from internet), my boiler does have the connected loop wire installed (at the boiler iteslf). Do I still need to remove it from the boiler panel even though the thermostat gets wired into the wiring centre?

 

[RandomGrinch]

Although not shown on photo above (I got that one from internet),

Which is one of the reasons why your original post didn't really make sense!

So what are your existing controls?
Do you have a separate programmer and thermostat?
Do you simply wish to swap your existing controls for a Nest, in which case, does your system currently work correctly?

 

[slpn1]

Yep sorry, that wasn't a great idea to send a stock photo. Here is my setup, showing the boiler wiring and the wiring centre box. The wireless thermostat has completely given up the ghost now so we are without heating. I know I need to remove the ribbon of the old controller. I assume IZ3 in the wiring centre is for central heating but can't see where hot water control would go. Everything I can find online shows the receiver being wired directly to the boiler. Not sure if it matters, but I bought a 2 channel Hive today rather than Nest as it does what I need and was on offer. Any guidance would be massively appreciated. I know I should get someone in to do it, I'm not being tight, it's really hard to get someone at mo, plus for most simplish things I'd do my own wiring, I'm just not 100% on the wiring for this.

Thanks again,
Simon

 

[RandomGrinch]

Ok, so your entire system is eBus.
This complicates matters, as the wiring centre is non-standard.
eBus has it's benefits, as it can better control (modulate) the boiler power, leading to slightly improved efficiency over an on/off stat, such as the Hive.

The straightforward solution would be to simply swap out your broken wireless stat.

The more complicated solution would be to decommission the existing wiring centre and start again with a standard one.
This is DIY'able, but I wouldn't recommended it for the inexperienced.

Here is a good introduction to S-Plan wiring....

S Plan central heating system

S-plan central heating system operation and wiring diagram

flameport.com

See if you can get a handle on it - this may influence your next steps.

Edit: looking again, you'd also need a new tank stat - your eBus system uses a temperature sensor; again better for efficiency, but not standard.

 

[RandomGrinch]

Just to add, if you are desperate for heating now, at the expense of having Hot water - you could try exchanging the wires in IZ2 with IZ1 and those in PZ2 with PZ1 (safely isolating the power first).
I believe that should give you central heating when hot water is called, but you won't have any thermostatic control.

 

[slpn1]

Thanks very much. Yep that would be way out of my comfort zone, but I think you've saved me from getting an electrician in to install the Hive I bought, only to be told it won't work. I would really like a smart stat so I can turn on and off heating whilst away and reprogram times easily. Do you know if there are any stats that would be compatible? I see Worcester do their own smart stat called EasyControl and I've read that Tadu ones are eBus compatible (most things I've read are people having issues getting it working). Or do you think it's best to get someone in to replace the wiring centre and tank stat? Thanks.