Nest 3rd Gen & Ideal Logic+ System 30

[Nintendofan]

I get the impression though that OT may have had its day, particularly in the UK. New domestic systems now have to be zoned [living areas / sleeping areas] Apart from the difficulty of having two OT connections to terminate, it would be impossible for two OT thermostats requesting different water temperatures to get that from the same boiler anyway!
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don't the newer Intergas boliers have 2 independent sets of OT connections, not sure how they work together though.

 

[fezster]

It's a protocol - and one which is not always implemented properly or completely by all manufacturers (boiler or controller).

One example would be that of a boiler manufacturer (I forget which one, possibly Veissman) who default their max temperature to some extreme amount (90 degrees plus?) when Evohome calls for max heat via OT. Obviously, this is not appropriate, and should be limited to 75 or 80.

You could argue it's the boiler manufacturer that should allow the max temp to be limited sensibly.
Or you could argue that Evohome should be sensible and call for an appropriate "max" temperature.

 

[PhilT246]

Interesting definition of OpenTherm from Wikipedia.

OpenTherm (OT) is a standard communications protocol used in central heating systems for the communication between a central heating boiler and a thermostatic controller. As a standard, OpenTherm is independent of any single manufacturer. A controller from manufacturer A can in principle be used to control a boiler from manufacturer B. However, OpenTherm controllers and boilers do not in fact always work properly together. The OpenTherm standard comprises a number of optional features and some devices may include manufacturer-specific features. The presence or absence of such features may impair compatibility with other OpenTherm devices.

So OT connections are the same and 'standard' yet different

I come from an IT background and it's not uncommon that "standards" are partially implemented or are extended beyond their documented spec either due to only implementing what you need or innovating beyond what's there today.

 

[shambolic]

SL2 in our boiler should be wired from HW off at clock and Cylinder stat. This then allows the outside weather comp to work.
The reason being if it’s a warm day and both heat and Hw on then weather comp will run the boiler at a lower temp so rads don’t get too warm but this means cyl won’t get to temp.
Once cylinder is satisfied power is sent down SL2 and the weather Comp is then allowed to be active.

 

[PhilT246]

SL2 in our boiler should be wired from HW off at clock and Cylinder stat. This then allows the outside weather comp to work.
The reason being if it’s a warm day and both heat and Hw on then weather comp will run the boiler at a lower temp so rads don’t get too warm but this means cyl won’t get to temp.
Once cylinder is satisfied power is sent down SL2 and the weather Comp is then allowed to be active.

Thanks shambolic. I'm not using weather comp. Is this response intended for this thread?

What I was looking to have was CH and HW using OpenTherm. I wired it all up and used the Nest Heat Link outputs for CH and HW to operate the vales only. The only connection to the boiler was using OpenTherm. With this setup the HW was only working when CH was on and the HW only reached the temp required for CH.

Possible solutions which need clarification are:
1. When using OpenTherm to control the boiler, the Nest should demand a higher temp from the boiler when HW is on. As far as I can tell it doesn't and HW boost doesn't work either.
2. Wire the Nest so that CH is using OpenTherm and HW uses the traditional switched live to the boiler. Ideal said they don't recommend this as the boiler might get confused.

Currently I have it wired up to do traditional switched live call for heat for HW and CH. Contrary to what Ideal told me, call for CH and HW do operate differently:
1. when there is a call for heat for CH (SL 1 IN), the boiler will only heat to the temp set on the temp dial on the boiler (In my case, 70 degrees)
2. when there is a call for heat for HW (SL 2 IN), the boiler will heat to what I presume is max temp (In my case, 80 degrees)
3. if there is call for CH and HW, then the boiler runs at 80 degrees.

 

[shambolic]

SL2 is for HW off not HW on. This then means the outside weather comp will work. that is the only use for SL2 as far as I’ve been told.
Don’t know what it does if weather comp not fitted. Although I do know it will bring boiler on at max temp as I’ve had one wired wrongly like that so I suppose you could use it to heat hw flow to 80deg if using end switches from HW zone valve into SL2. meabs that if heating and hw on together roads will get to 80deg.
set hw an hour before heating so it’s off then open therm can look after ch.
if that’s how it’s working for you then fine.

 

[shambolic]

But I can’t see how that works as 240v down SL2 lets the low voltage and weather comp control boiler. As no voltage on SL2 makes boiler run at 80deg to heat cylinder. (And open therm is off the same side of the controls). I’ve never tried it but SL2 will bring the boiler on even if no voltage in SL1 which makes it over heat as normally all end switches from valves are wired into SL1 to bring boiler on. (If no weather comp)
so if SL2 has 240v boiler will come on but don’t know how that works with open therm. Wait 2month and buy our halo controller that controls zones and hw and ch done on phone and controller all using opentherm. (Apparently)

 

[PhilT246]

set hw an hour before heating so it’s off then open therm can look after ch.

I like that idea, it's a potential solution.

 

[PhilT246]

But I can’t see how that works as 240v down SL2 lets the low voltage and weather comp control boiler. As no voltage on SL2 makes boiler run at 80deg to heat cylinder. (And open therm is off the same side of the controls). I’ve never tried it but SL2 will bring the boiler on even if no voltage in SL1 which makes it over heat as normally all end switches from valves are wired into SL1 to bring boiler on. (If no weather comp)
so if SL2 has 240v boiler will come on but don’t know how that works with open therm. Wait 2month and buy our halo controller that controls zones and hw and ch done on phone and controller all using opentherm. (Apparently)

The manual seems to imply that SL1 IN is for CH and SL2 IN is for HW (https://idealboilers.com/uploads/documents/logic-system-s-installation-and-servicing.pdf page 34)

The LCD display seems to reflect this too:

I fear that we're not getting to the right people at Ideal who actually know how this stuff works....

 

[shambolic]

That’s internal wiring. It’s external you’ll need. I’ll get wiring instructions for use with weather comp. you then need to know if the function is different if no weather comp fitted.

 

[PhilT246]

you then need to know if the function is different if no weather comp fitted.

The weather comp wiring takes me deeper into the rabbit hole... It's unlikely I'll ever use weather comp so your statement above puts me back to trying to understand the logic that's built into the boiler when switched live HW and OpenTherm CH are used at the same time.

I might return to pure OpenTherm and do some more testing to try to understand why HW boost wasn't working previously.

 

[GoodDIYjob]

I'm chipping in because I have some experience of a nest gen 3 in y plan set up (non opentherm) and also a lyric T6RW set up with two zones on s plan with opentherm.

I am not an installer but I am not too bad with understanding control systems.

Anyway, I was surprised to find out that there is no 2 zone option with nest and opentherm. And if I am reading right not even HW and 1 Zone in an S plan set up. That does seem a bit crazy given the trouble they went to tailor the gen 3 to the UK rather than solely re release a NA market product.

With the Lyric T6RW 2 zone S plan on an intergas eco RF boiler both thermostats talk to the boiler via Opentherm and appear to mediate between themselves so that the highest demand thermostat negotiates the message for flow temp to boiler.

Now my understanding is, but I have not tested because I don't have a DHW tank (I use the intergas in combi mode), that if you ask for HW timing simultaneously it uses the preset max flow temp set up in the boiler whilst the HW demand is active.

Surely, that is exactly what Nest should have set out to do?

I'm left wondering if it is just an oversight that could be implemented with software coding update if Nest realise and can get feedback to the right person that it is an oversight?

 

[PhilT246]

Now my understanding is, but I have not tested because I don't have a DHW tank (I use the intergas in combi mode), that if you ask for HW timing simultaneously it uses the preset max flow temp set up in the boiler whilst the HW demand is active.

Surely, that is exactly what Nest should have set out to do?

I'm left wondering if it is just an oversight that could be implemented with software coding update if Nest realise and can get feedback to the right person that it is an oversight?

100% agree. I have asked https://support.google.com/googlenest/thread/22111592?hl=en but Google seem more concerned about which country I'm in....

 

[PhilT246]

I've just spoken to Nest support and they have stated that the "Nest does not support hot water with an OpenTherm system boiler". They suggested I get a different controller.

I asked them to open an enhancement request (Software change) and also state clearly here (https://support.google.com/googlenest/answer/9259578) that it's not supported.

Thanks for the help everyone. I'll report back if my enhancement request progresses....

 

[GoodDIYjob]

Well done on the persistence and good luck. BTW, your new support request link to make the changes does not link through, I don't know if that is because they have not accepted it yet or some other issue when you posted it.