Separate Zone for UFH on Vaillant system

7 Jan 2010
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United Kingdom
I have a Vaillant ecoTEC plus 637 system boiler, a uniSTOR unvented cylinder, a VRC 430 weather compensator & thermostat all connected through a Vaillant VR 65 control centre.

I've just had underfloor heating installed in a new extension and I want this connecting to the existing system such that it is on a separate zone with its own thermostat. The plumber isn't familiar with Vaillant control centres, so I'm trying to gather information for him (and so I understand what he needs to do, to ensure it is done correctly).

From what I can gather, the VR 65 control centre can only handle a single independant heating zone as well as the hot water control.

The VR 61/3 appears to handle two heating zones as well as hot water, but I'm not sure what the difference is between the VR 61 and VR 65 and I'm struggling to find documentation on the Vaillant website.

Can somebody please advise what needs to be done to add a 2nd heating zone to my setup, ideally making use of weather compensation (a 2nd heating curve?).
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I wouldn't advise using a regular zone valve.

Either use the individual actuators designed for the manifold or something like guardian solutions smart zone valves.

Standard valves are not rated for continuous use and will seize up sooner or later.
So far my research suggests my existing VR 65 control centre will need to be replaced by a VR 61, which provides control for direct hot water and "two" heating zones.

If this is definitely the case I'm confused about why the VR 65 was used for my system, which was installed about 4 years ago as clearly the VR 61 is superior.

I assumed the VR 65 was a later model than the VR 61 (I'm from an IT background, so familiar with higher numbers being later versions :D ), but I have noticed the VR 65 is now obsolete.

I've also noticed there appear to be different models of the VR 61 e.g. VR 61/1, VR 61/2, VR 61/3, VR 61/4. Are these simply newer versions or are they completely different products?

While I'm able to find information on the Vaillant (Commercial) website for the VR 61 there's no explanation of these different "versions" and the VR 65 isn't listed.

I'm a little concerned that my VR 65 may include functionality that I would loose if I switch to a VR 61 and just want to be sure this isn't the case.

Would it be a simple case of switching the VR 65 with a VR 61 (I can see the terminals are labelled differently) and would my VRC 430 thermostat need to be re-programmed (it should recognised CH2 as well as CH1), assuming my VRC 430 is compatible with the VR 61.

I have fired off a number of questions to Vaillant technical support, but so far got no reply.
No help on this! Never mind.

Having spoken to Vaillant technical support and Wunda Floor Heating TS (the supplier of the UFH), I now know exactly what is required:

- VR 61/4 to replace VR 65
- VR 81/2 remote thermostat, which will interface with the existing VRC 430 to give a 2nd heating zone (CH2)
- Zone Valve adequate for requirements of UFH

I've given up on my builder and his plumber and I'm looking to employ someone to make the changes who is familiar with Vaillant kit.

Anybody out there near Wetherby (North Leeds), with Vaillant experience, who would be interested?
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I have a similar system with a system boiler and unvented cylinder, you will need a motorised mixer valve that connects to the VR61/2 for the UFH circuit so the system can run two separate flow temperatures on the heating circuits, you can then set the different heating curves from the 470f controller (I assume the 430 controller will let you do this).

This system works very well as it can run three separate temperatures for HW and the zones, so I still get the rapid recharge of the cylinder with 80c flow temps, the heating circuit can run on a higher curve than the UFH which runs on a much lower curve. The UFH can also remain on when the system is heating hot water

It is a complicated system to wire up so make sure you get a good heating engineer to do it, the pump on the UFH needs to be wired back to the VR61/2 aswell as a VR10 temperature sensor added so it can regulate the flow temp.

On a side note the VR65 has been replaced by the VR66 this supports two zones and a cylinder but doesn't support a mixer valve so the two heating zones run on the same heating curve/flow temperature.
No help on this! Never mind.

Having spoken to Vaillant technical support and Wunda Floor Heating TS (the supplier of the UFH), I now know exactly what is required:

I have to say that I don't think you do understand what is required.

You need a mixer valve as Hoss has explained very clearly.

Although they are really very simple there are few heating engineers who are very familiar with them.

Agile, I beg to differ. The manifold already has a mixing valve and a pump fitted.

I have a Vaillant engineer visiting this afternoon, so I'll be able to talk through the setup with him.
Hi hossacd, I've just noticed your post (don't know how I missed it) and now I understand what Agile is saying. Thanks for the information. I had wondered what a VR 66 did, but the VR 61 was specifically mentioned by Vaillant as being the correct wiring centre.

I will discuss this setup with the engineer this afternoon.

I have a document (AIUFH2) from Vaillant, which I plan to give to the engineer. I hadn't appreciated the difference between a zone valve and mixing valve and the manifold is fitted with a blending valve, which I guess is different again.

The vaillant document also shows a low loss header, but I'm not convinced this is required in this single boiler, residential setup, but again, I'll discuss this with the plumber.
Hi hossacd,

You don't mention a Low Loss Header in your setup, so I guess this wasn't necessary.

I only mention it as another poster with a similar setup had one installed and Vaillants AIUFH2 document also shows one.

Also, did you install a thermostat in your UFH zone and if so which one? (was it the Vaillant VR 81, which ties in nicely with the VRC 430?).

You mention a VR 10 tempearture sensor (which comes with the VR 61). Where did you connect this?

I would upload the AIUFH2.pdf document that Vaillant supplied, but there doesn't seem to be any way to do it.

You got me wondering what the difference is between a mixing valve and a blending valve. From what I can gather the term blending seems to be used with UFH, but I think they essentially do the same thing.

My manifold came supplied with a pump and thermostatic blending valve on the flow side. So, I suspect only a zone valve would be required at the point at which the UFH flow pipe has been connected to the existing CH flow pipe and this would simply allow water to the manifold/UFH whenever it was called for. The blending valve on the manifold would then control the temperature of water being pumped through the UFH pipes. Is this correct? Here are some details from a fact sheet I downloaded:

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Hi Milleniumaire
I just posted in your other famous thread, lol.#
Listen it seems that the document AIUFH2.pdf you have it could help me/my HE? If you are unable to post here then perhaps can you PM me?
Your first diagram shows a thermostatically controlled blending valve. That will give rather basic temperature control although always hampered by the long time constant of UFH.

A blending and mixing valve are essentially doing the same thing as far as the water is concerned.

But a blending valve is usually called that when it has its own temperature control on it. They in the basic form provide a constant temperature of water out.

Yours is a step higher and gives an output temperature inversely proportionally to the room temperature.

But when we refer to a mixing valve in this context then we mean an electrically controlled proportional valve!

Hope this explains it.

My system doesn't have a low loss header, it is a variation of hydraulic drawing 2 & 4 in the fitting instructions linked below, it has a mixer valve and vr10 on the secondary heating circuit with zone valves on the HW and heating circuit 1.

The instructions aren't great it advises before the diagrams that they show a full system and some parts are optional but doesn't tell you what parts are optional.

I have read a few recent posts where Vaillant have advised a low loss header is required, they may have changed something that requires one. You would need to confirm this with them, although I can't see what having a low loss header would gain in a residential system.
The purpose of a low loss header is to ensure adequate and more constant flow rate through the boiler.

In itself it does nothing for the house heating but just enables the boiler to work better.

If there is no LLH then an autobypass valve is needed but these can reduce the differential across the boiler.

The Vaillants are particularly sensitive to flow rate problems. Its no problem if the system is properly designed though.

I recently installed my own UFH comprising two Wavin (renamed Hep2O was Thermoboard!) manifold sets each with a number of floor loops with electric actuators to control the loops using individual wifi room thermostats via a Wavin control box which manages the UFH systems.

There are two UFH mainifolds due to the large floor area and structure of the house that limits pipe routing to two distinct sides of the house which is a split level bungalow. There is also a separate radiator circuit for WC and bathroom towel rails and the cellar. There is a temperature/mixing contol valve on each UFH manifold to control (limit?) the UFH flow temperature.

I used a LLH to 'hydraulically' separate the UFH and rad zones whilst allowing the boiler (Vaillant 937 Combi) to manage its own primary circulating water temperature. There are no additional Vaillant controls or mixing valves. This works well and ensures one circuit does not rob the other which may happen if you just split off the flow /return pipes. It also requires no balancing between the major circuits as each draws its needs from the LLH and returns to it. The rad zone has its own pump and motorised valve to enable the towel rails to be on/off as desired.

Oh and the LLH allows me to add a heat pump to the system later. :LOL:

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