Vaillant heat only boiler + switched live thermostats + weather comp?

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Hello lovely people

I have Valiant 428 heat-only boiler on S-plan Plus pipework.
3 heating zones are controlled by 3 Nest thermostats via Switched Live Terminal 4.
System water temperature is set at constant 45C.
Lovely config.

Now can I add Vaillant eBus Weather Compensation product (VRC series?)
to this Switched Live controlled boiler?

I want to have the flow temperature of system water
to be dependent on outside temperature.

Ideally, a product that sits in the boiler fascia,
takes outside temperature from Internet via Wi-Fi,
and sets the system water temperature automatically via eBus.

Any Vaillant gurus here?
 
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Replying to myself.

Wanted to document the fact that Vaillant boilers will work with switched live thermostats (Nest),
with hot water cylinder charging activation via switched live thermostats (Nest) <-- (click this link for detail)
AND with weather compensation mounted on fascia (VRC module) to adjust hot water temperature depending on outside temperature.

So:
1. Your heating is running at low temperatures depending on outside temperature (I get great results with curve 1.25).
2. When your hot water cylinder is calling for charging the boiler is going all the way up to 80C (and according to Nest's hot water schedule)
3. AND all your thermostats in the house are switched live Nests

Vaillant UK will tell you this does't work.
It's BS -- everything works perfectly.

All you need to do is to buy weather compensation VRC device that was manufactured at time when your boiler was released and mount it on boiler fascia.
VRC module (in my example VRC 470) will regulate your hot water temperature and will allow to adjust all related parameters of the heating curve.

Any questions you may have I'll answer here.


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Hi notorious.

Just read your thread. Interesting! :)
I have a simlar (but smaller) boiler (418 ecotec plus) fitted in 2011.
Id like to add weather comp, and this looks like you've done that?
Please could I ask what you have on the ebus? I have not used it at all, I just have 240 v onto 2 x valves, one for DHW and one for our single zone CH. Timer for DHW, programable room stat for CH.
The current Vaillant programmers / stats aren't compatible with our old boiler (so tech phone support said today), so looking for any ideas to improve it based on 'legacy' kit.

Thanks for reading, any help or insparation gratefully received.

Thanks.
 
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Hello,

I only have VR65 on eBus
You will also need VR65 that to install weather comp.
(VRC 470 is in boiler fascia, but technically also on eBus)

Why you need VR65?
Because in weather comp mode your boiler will run in low temperatures and will be unable to heat hot water cylinder.
Hot water cylinder needs to be heated with higher temperatures when cylinder thermostat is calling for heat.
So, you need VR65 to run boiler in dedicated DHW mode when cylinder calls for heat. In normal hating mode your weather comp will run in low temperature.

How to install VR65?
Here's the tread about it:
https://www.diynot.com/diy/threads/vr65-vr66-for-hw-flow-temp-control.494071/
 
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Thanks for the quick reply.

I guess the flow temp to radiators is based on the weather compensator (and it's settings) and the flow temp for charging DHW is from the boiler control knob then?

Does the nest (s) link to the ebus at all then? I guess they just drive the zone valves with 240 V.
 
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>> the flow temp to radiators is based on the weather compensator (and it's settings)

Yes

>> and the flow temp for charging DHW is from the boiler control knob then?

Nope.
DHW charging temperature is stored in d-register (don't remember exact number).
Open boiler manual and you'll find it.
By default 80C I think but can be increased to 90.
That value can be changed via both boiler screen and via VRC menus.

The knob is used to set **target** temperate of the cylinder if you use analogue temperature sensor, not the On/Off thermostat. Because we use On/Off thermostat the boiler's software will treat the knob as On/Off switch for DHW heating. When knob is in Zero position the boiler won't service eBus request for hot water. Knob in any non-Zero position will give green flag for DHW charging mode.

>> Does the nest (s) link to the ebus at all then?

Nests only do 240v stuff. Nests know nothing about eBus.
Nest drives valves and valves, when fully opened, send 240v to RT ("remote thermostat") terminal on boiler to initiate heating mode.
As you have it now in your current system.

One of your Nests will have DHW schedule and a 240v switch for that.
That switch will send 240v to open DHW valve. Your cylinder thermostat sits before that switch.
When fully opened, DHW valve's microswitch will connect together two terminals in VR65 box (those terminals are for connecting to cylinder thermostat) and VR65 will issue comnand via eBus to the boliler to initiate DHW heating mode.
You haven't yet experienced that mode in your current setup.

If boiler receives both 240v on RT for heating and eBus command for DHW charging the cylinder charging mode will take priority. When DHW charging is finished the boiler will return servicing RT request.

You can install a simple relay to close heating valves during DHW charging even if Nests demand heat during this time. Very simple. Or you should accept the fact that your radiators will run hotter during DHW charging.

When cylinder thermostat satisfied, it will interrupt 240v line, the valve closes, interrupting the VR65's terminals and another eBus command goes to boiler to switch off DHW heating mode.

Essentially, VR65 works like a box that translates your switched live 240v into an eBus on.off commands to initiate DHW charging mode.

Read discussion here for more detail:
https://www.diynot.com/diy/threads/vr65-vr66-for-hw-flow-temp-control.494071/

Get your VR65 on eBay for £10 and enjoy the new life.
 
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That's great, thank you for taking the time to explain it, I appreciate that. (If you don't already) youshould work for Vaillant.
Right, let's find ebay... :)
 
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"All good things come to those who wait"

Search for VR66 too.
VR66 can work in VR65 mode.

People remove stuff because the migrate to comb boilers and put them on eBay for pennies.
Search gumtree and Facebook marketplace too.

Save the search so that eBay will tell you when it becomes available.

Do the same for VRC 470 (wired or wireless). I use wired.
 
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"All good things come to those who wait"

Search for VR66 too.
VR66 can work in VR65 mode.

People remove stuff because the migrate to comb boilers and put them on eBay for pennies.
Search gumtree and Facebook marketplace too.

Save the search so that eBay will tell you when it becomes available.

Do the same for VRC 470 (wired or wireless). I use wired.

Hmmm, interesting, Vaillant tech support told me my 2011 ecotec plus wouldn't work with VR66.

Good call on the saved search idea.

Thank you.
 
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>> Vaillant tech support told me my 2011 ecotec plus wouldn't work with VR66.

There's a switch on VR66 that makes it VR65 for compatibility

Buy yourself VR65 for £5 from Facebook (link above) and done.
 
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>> Vaillant tech support told me my 2011 ecotec plus wouldn't work with VR66.

There's a switch on VR66 that makes it VR65 for compatibility

Buy yourself VR65 for £5 from Facebook (link above) and done.

A switch for compatibility. Nice.

Ive asked if the one in Camberly can be posted. Fingers crossed!
 
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