NEST controlling Pre-heat function on WB 30i

[Taser]

Hi all,

My WB 30i combi obviously provides DHW on demand at all times when a tap is opened.

It has a preheat function to provide a small amount of pre-heated water to reduce DHW heating times - manual control is via the ECO/PREHEAT button.

It also has a (usually linked) input to presumably allow the preheat function to be enabled/disabled via external controls.

Am I correct in saying that if I configure NEST as a 'System' boiler instead of 'Combi', wire a live supply/DHW switch using N/O terminals 5&6 on the NEST Heat Link and remove link on the boiler, that I will then be provided with direct app control (and importantly, schedule) for the preheat function?

If this is indeed possible, does having the NEST set as 'System' affect any thing else that may be detrimental to my combi boiler?

Thanks

 

[stem]

If you are referring to terminals 'L OUT' and 'LR' (with the tap symbol) as below, those terminals are provided for external time control of the hot water pre-heat function.

The highlighted link is removed....

....and the terminals can then be connected to the Heat link 5 & 6 instead as you figured.

With some types of boiler it is necessary to open a 'room sealed' compartment to access the boiler's wiring terminals, where this is the case, this is not a DIY job and should only be done by a RGI (Gas Safe Engineer) who can carry out the necessary safety checks to make sure that it is properly sealed up again afterwards. I can't remember if your boiler falls into this category or not.

Configuring the Nest as a 'System Boiler' enables the hot water control functions, the heating doesn't work any differently. I seem to remember that the boiler switch needs to be left on the Pre-heat selected setting and not Eco.

 

[Taser]

Brilliant, thanks for your rapid and comprehensive reply - very helpful.

 

[sheridat]

Taser assuming that you did wire this up could you confirm that the boiler needs to be set to that the boiler switch needs to be left on the Pre-heat selected setting and not Eco

 

[Taser]

Sheridat, yes, you are correct. This is how I understand it.

Firstly, my Nest integration works exactly as I intended it to. I set up the nest as a 'System' boiler which enabled a new set of options to control 'Hot Water' within the Nest app and the ability to set a schedule for preheat mode.


This is how the logic works:

With the link in place, the boiler can be manually toggled between preheat off (shown as Eco) and timer mode (shown as Preheat) with a 1 sec push of the selector button.
Of course, as the link is in place, there is no timer and therefore it is forced into preheat being on.
Simply put, preheat is either on or off and is controlled manually from the boiler panel. The state of this setting seems to be remembered if the power is disconnected.


With the link removed and replaced by the timer/Nest, when the boiler is on not in Eco mode, the preheat state is decided by the Nest.
So now, preheat is either off or timer controlled.
The manual toggle of these states has priority over the Nest.
If you manually set it to off on the boiler panel (Eco) it stays off, whatever the Nest tries to demand.
If it is on then it is up to the Nest whether preheat is on or off and this is shown by either the preheat display or the new display of Eco with a timer icon after it depending on what the Nest is demanding. The Eco with a timer display indicates preheat is currently off but that the state will change automatically via the Nest.


It's amazing how such a simple answer has turned into an essay but that's probably saying more about how my mind works! I hope that explains it in detail and wasn't too confusing. Let me know if you need to know anything else.

 

[sheridat]

Thank you for the rapid and detailed reply. I have a WB 8000 Life combi providing heating to our UFH and Towel Rails. The UFH is controlled by 7 Heatmiser Neostats/Neohub/App and the Towel Rails by Honeywell's EVOHOME system with Smart TRV's on the Towel Rails. The Honeywell controls can be controlled via the internet as can the Heatmiser's. Both sets of controls use the 230V LR (Heating symbol) to demand heat.

WB have this (perhaps misleading) page on the web that suggests that if you have a twin channel programmer attached to your combi you can have timed preheat - https://www.worcester-bosch.co.uk/s...rogramme-hot-water-times-with-my-combi-boiler rather than constant on or off.

It just so happens that in the Boiler room there is a twin channel programmer this is not connected to anything. My basic idea is to get my heating engineer to
1. Provide power to the digital programmer;
2. Connect the "HW on" to the LR (tap symbol)
3. Not connect the digital programmer "CH on" to anything
4. Switch "Eco" off (probably do that before anything else)

The only thing that worries me about this scheme is that my heating engineer who is an accredited Bosch Installer seems to know absolutely nothing about this functionality and has never done a similar thing for a customer with either a single or twin digital programmer. My assumption is that normally this "capability" is "exposed" to customers when WB controls are fitted.

Thank you again for the logical analysis of the events needed to get this to work!

 

[Taser]

You'll have to let me know how the EVOHOME system is for you. A future upgrade for me will be to get some SMART tops for my existing dumb TRVs.

Now bear in mind I'm not a boiler engineer but I have been an electronic engineer all my working life so am competent in some respects. I did my research thoroughly and when my boiler was installed (also by a Bosch accredited fitter) I explained my plan to him and he said, he had never done anything like that before, NEST couldn't do it, etc.. etc... So maybe our combined experiences suggest most fitters want to do what they are good at but not entertain any deviation from the norm - which is fair enough.

It turned out to be very straightforward and thankfully, WB allows wiring access without disturbing the 'room sealed' compartment that stem refers to above (which I wouldn't touch with a barge pole, obviously).

Your link to WB's page suggests that your boiler's preheat functionality is similar if not identical to mine. Any device that can switch a 230V feed to the LR (tap symbol) will operate your preheat function the same as mine, so your spare timer should be fine. As you say, just ignore the CH part of it.

Even if your fitter doesn't yet understand what you want to achieve, you have explained it perfectly to me so surely he would be able to wire that for you?
All you need is a power feed from the boiler to the timer and a switch return live to the LR terminal - could all be done with one flex if you could source a few metres of 4 core flex. That way, the timer's 230V supply would come from your boiler - which means that if you ever need to isolate power to the boiler, everything is safely de-energised and there are no unexpected lives floating about.
Only you know what you are comfortable/competent to do though

Either way, I hope you sort it out to your liking.

 

[sheridat]

I wrote to WB's Technical Advice email address and they confirmed that basically you need to switch eco off - so that's great.
Regarding controls and radiators - I wonder if you have had a look at Bosch's new "Easy Control" setup? It comes in two flavours - Wired to the EMS bus on your boiler or if you have an 8000 Life/Style and perhaps others via an RF dongle that literally goes inside the boiler's bottom.

I am temporarily using it via the dongle to control my towel rads (4) until my heating engineer comes on Monday to wire up my Heatmiser/Evohome controls(*) - warm enough to not need heating at the moment.

The Easy Control acts as a Smart Thermostat for the room it is located in and can also control Bosch Smart Thermostat heads. The virtues of using Easy Control is that it talks Bosch UK EMS which nothing else does. Feature packed:
1. Your smart TRV's demand will in effect modulate your boiler (I think)
2. It uses your location to drive weather compensation control if you choose
3. Has home presence detection
4. An app so you can control your heating from anywhere
5. Optimum start/stop
6. Some control over your hot water (but I haven't researched that)
7. You can put into it what your gas per Kwh cost is and it will produce usage stats for you and display graphs etc - you can export the data - see attached zip file that contains the csv file that the export function produces.

* I really like it but currently it cannot be used to drive my UFH - Bosch tell me an "adapter" is in the works to do so so I have to stick with my current controls for the moment.

The Evohome is a quality piece of kit especially the HR92 TRV's but if you have a WB boiler they drive it using a simple on/off relay that you connect to the boiler via LR (CH) or a 2 port valve that switches the boiler on. So NO modulation. The controller allows you to control each TRV individually in both timed mode or temperature mode. We only use our en-suite and cloakroom on a regular basis so they are on a daily schedule and the other two are set to come on if the temperate ever drops below. Great support can be found at a place called the Evohomeshop https://theevohomeshop.co.uk/

A Honeywell Evohome setup from them with 4 TRV's that have a display (HR92's) is £469
A WB Easy Control starter kit (three trv's) and 2 extra trv's roughly the same price.

I would go for the WB controls. I've quickly tried to check Easy Control is do able with your boiler model but of course you would want to check the whole thing out yourself.

I will let the heating engineer do the work - I can change a plug but otherwise I am frightened of electricity - I've shocked myself half a dozen times over the last 64 years.

Thanks once again!

 

[Taser]

Thanks for all that interesting, detailed info. I will certainly look into SMART TRVs somewhere down the line.
Make sure you add a post when you get your preheat working.

Good luck.