VR65/VR66 for HW flow temp control

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I'm finally getting around to tackling the problem of pairing a non-Vaillant unvented cylinder with a 438 boiler. The goal is to be able to reduce the flow temperature during the summer, but have the cylinder heated at MAX temp (80 degrees being the default, I think).

I had a previous post on this and was given some useful info:

https://www.diynot.com/diy/threads/vr65-with-on-off-heating-and-hw.388359/#post-2986084

This indicates that the VR65 (or VR66) relies on an appropriate Vaillant ebus thermostat/programmer to control timings for HW.

However, is it the VR65 which instructs the boiler to increase the flow temp to 80 degrees when the 240V cylinder thermostat terminal is closed? And will it do so without the corresponding vaillant controls attached to it.



If so, would it be possible to link the HW zone valve SL to the CYL terminals, which would allow me to use my existing programmer for HW timings and the existing cylinder stat and overheat stat in the Megaflow, and have the VR65 instruct the boiler via ebus to boost the flow temp whenever the CYL terminals are closed?
 
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For anyone else interested in trying this - The zone valve can act as a dry contact relay, using grey and orange to the CYL terminals on the VR65. Just ensure the grey is no longer supplied with mains voltage.

The VR65 will boost the flow temp to 80 degrees, but it's not clear if it will do so unless the rotary dial on the front of the boiler is set to 80 also. This would defeat the purpose of what Im trying to achieve. Previous posters have suggested that the VR65 boosts to 80 on HW demand regardless of any other setting, but others say the boiler control acts as an upper limit, and no ebus command can override it.

So in the absence of another controller to instruct the boiler to lower the flow temp, this probably will not work.
 
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fezster,

I can confirm that VR65 will work exactly as you originally described.

HW flow temp control via eBus works perfectly with traditional switched live (SL) controls like Nest.

SL controls are not mutually exclusive with eBus controls.

Boiler will satisfy both demand from eBus and from SL terminal 4. Boiler software will work in hot water priority (make sure d.70=0) in case both heating request (via SL) and hot water request (via eBus) are received.

VR65 works as a box that instructs the boiler to increase the flow temp to 80C degrees (to be precise, to the value from d.78) while the cylinder thermostat terminal (CYL) on VR65 is closed. As soon as CYL is open again VR65 will instruct the boiler via eBus to exit the hot water heating mode.

HW temperature knob will work as On/Off switch for hot water control. Off in position zero. On in any non-zero position.

Don’t know how I’ve lived without this feature.

Attached is picture for VR65 wiring.
Notice no valves are connected to VR65.

Very simple.
 
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View attachment 209685 Fezster,

I can confirm that VR65 will work exactly as you originally described.

HW flow temp control via eBus works perfectly with traditional switched live (SL) controls like Nest.

SL controls are not mutually exclusive with eBus controls.

Boiler will satisfy both demand from eBus and from SL terminal 4. It will work in hot water priority (make sure d.70=0).

VR65 works as a box that instructs the boiler to increase the flow temp to 80C degrees (to be precise, to the value from d.78) while the cylinder thermostat terminal on VR65 is closed.

HW temperature knob will work as On/Off switch for hot water control. Off in position zero. On in any non-zero position.

Don’t know how I’ve lived without this feature.

Attached is picture for VR65 wiring.
Notice no valves are connected to VR65.

Very simple.
Given that this post is 3 years old, I expect they've got it sorted by now
 
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Thanks for posting this I've dusted off my VR65 which I gave up on a couple of years ago because...

I didn't really want to use the NTC supplied
I wasn't keen on having to connect up the 3 way valve to the box
and I preferred my old mk2 Nest to the vaillant ebus room thermostat.

Having set the partial DHW load D77 to 12 kw for testing I love how the boiler now starts up very gently to heat the DHW and if it does ever fail to reheat the cylinder completely in one burn it should at least restart without continually overshooting.
 
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Glad you liked it brother.
I personally find it amazing.

So stupid that Vaillant don’t advertise their VR65/66 as a simple box that converts external on/off contact to eBus commands that switch on/off boiler to heating mode :) They miss huge market opportunity in this country.

Let’s see if more people will follow!
 
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I got mine reasonably cheap with the intention of trying to monitor the ebus commands it sends to the boiler to activate the DHW mode.
That project didn’t work out although I still have a raspberry pi hooked up to the bus and that can send a variety of other commands to the boiler.
I’d still really like to know the sequence of commands to start and stop DHW heating.
 
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What stops you now from logging all eBus traffic?

Hope OpenTherm will prevail eventually.
 
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I tried logging the communications using ebusd some time ago and failed to find anything that looked promising so I gave up and settled for simply changing the flowsetmax temperatures, as required, for heating/DHW.

I may have another shot at it now the VR65 is connected again.
A nice little lockdown project. :(
 
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Gotcha.

Well, since we now know VR65 activates proprietary cylinder charging mode via classic switched live controls I’m quite happy to be deprived of knowing the mystery of eBus commands behind the scene :) :)

Good luck with your lockdown project.
Hope you’ll crack the code this time.
 
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I assume you need the vaillant control (eg. VRC 470 as per your other thread) as well as the VR65/66? Otherwise, how do you lower your flow temp?
 
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That’s right.

VR65 to active hot water mode via simple on/off switch and VRC 470 to activate weather compensation (flow temp control for heating). VRC’s thermostat feature is automatically deactivated if it’s installed in the boiler facia. So VRC 470 is not controlling temperature in the house and is not issuing any on/off commands. It's sole function is controlling water temperature in heating mode via outdoor sensor. Effectively VRC 470 and VR65 are becoming part of the boiler providing the missing capabilities.

No Vaillant controls in rooms.

Everything is driven via Nest’s on/off controls. Vaillant stuff is in the “back seat”, in the boiler closet. Where no one can see them and where they belong. There's no misalignment here.

VRC 470 is an additional extra. You don't have to install it if you only want VR65 for your proper HW control. In this case heating flow temperature will be controlled by a knob, as before.

More detail about weather compensation is here
https://www.diynot.com/diy/threads/...switched-live-thermostats-weather-comp.557514
 
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Nice.

From your picture, you have grey and orange going to the CYL terminals on the VR65. Where are these taken from? And do they have any voltage on them?
 
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Fezster, -- grey and orange are connected directly to the microswitch of the valve.

VR65 is capable to determine if grey and orange wires are opened or connected together and activates hot water mode if connected together.

No voltage on them! :)
 
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