Vaillant VR65 and Ecotec plus - diverter valve position

22 Sep 2003
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United Kingdom
I have just had a Ecotec Plus 618, VR65 and Unistor retrofitted into an S Plan system, controlled by a VRC 430 weather compensator.

The installer has set the diverter valve on the boiler (diagnostic level d70) to the mid-position, enabling simultaneous demand from both heating and water.

However, if the cylinder is calling for heat (i.e. cylinder temp is below target temp) during a programmed 'dhw on' time window, there is little response from the boiler unless I manually force the heating on (from 'auto' to 'manual').

Otherwise, the boiler goes rapidly from s24 (cylinder charging, burner on) to s28 (anti-cycling) and doesn't charge the cylinder.

Likewise, in the evening (when both DHW and CH are programmed on), the heating won't start firing (s4) until the programmed DHW window closes.

What's wrong here? It seems to me that only one of DHW and CH can be charged at any one time, despite the correct d70 diverter valve setting of 1 being set at the boiler.

Both CH and DHW zone valves seems to be wired correctly at the VR65, as does the cylinder NTC and boiler-VRC430 ebus connections.

Simond, Gas4You - help please! Installer is coming Monday.
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Firstly, we have not yet fitted VRC430 (1st one in two weeks time) as the last one was a VRC400, (as Vaillant are often late bringing out promised products).

Furthermore we have not tried to bypass the priority system, because it negates some of the benefits of a weather compensated system, which is why one would fit the VRC400 or 430 in the first place.

You may find that the boiler manual was not written for the VRC430 and there may be a software incompatibility. In other words, it may be a feature that isn't available.

You suggest that the boiler cycles when in DHW mode. This suggests that the valve is not opening. You need to check that the cyl stat is working, is this the thermister or a third party stat you are using with VR65??? Try bridging the terminals on the VR65 for the stat.

The obvious thing to do before getting too much into the detail is to revert the boiler to default settings and see whether it is happy controlling the DHW and HW. If it is, you either have a software problem or your installer has fitted a diverter, rather than a mid position valve.
Just re-read your post. I had assumed you had an ecoTEC and a conventional cylinder with a 3port.

If you have two separate zone valves and a UniSTOR then I guess you are using the Vaillant thermistor in the uniSTOR and not the wired conventional stat?

And when you say you manually opened the CH valve, I guess you mean the HW valve?

As before, i would set the d setting to default and see what happens. Check your installer hasn't wired the thermistor and the cyl stat in together.
Thanks for replying. I have not touched the zone valves on the pipework. I have only 'forced' the heating to come on using the VRC 430 software.

Yes: we have two separate zone valves and the VR10 NTC in the Unistor, in place of the cyl stat (which was removed and discarded - I binned it!). I have reset boiler d70 to default (warm water priority) and turned off heating using VRC 430.

The boiler doesn't respond when I set the cylinder target temp to 70 degrees, even though the actual cylinder temp is only 55 degrees.

Does this suggest the DHW zone valve on the pipework is broken?
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It could, yes.

The VR65 does not 'read' the pin switch on the motorised valve and therefore assumes it is open when the live wire is connected.

Set the boiler to HW and manually open the HW zone valve (it is piped to the cylinder 'flow' connection) using the lever on the side, it can usually be latched in the open position. The boiler should then fire and run heat into the cylinder.

If this works I suggest you then get a multimeter and check the connectors in the VR65 are sending 230v to the valve. Or, swap the cables from the HW to the CH and vice versa. NB: There should only be three wires (earth, neutral and phase) connected into VR65 from each zone valve. The grey and orange (sometimes also white) wires should be insulated off.
There are certainly only 3 wires from each zone valve wired into the VR65 - live, neutral, earth. Other wires from valves are isolated, yes.

Don't have multimeter so will have to wait for installer (now tomorrow).

I have a hunch it's all working as it should - it's just too complicated for me to understand compared to my old 'on demand' S plan.

I will be interested to hear your experiences in configuring your first VRC 430!
I have fiddled with a VRC430 at Vaillant HQ. Ooh er missus.

The VRC430 is an awful lot easier to use than the VRC400, which does the same thing but in an even more hopelessly complex Germanic way.

We were very wary of fitting the VRC400 because of all the callbacks. People never could understand what it was doing. Sound familiar? :LOL:
From what I can tell the problem lies with the installer setting d70.

When you say you have reset it to 0 did you actually hold the i button in until the 0 disappeared? If not it would have not been stored.

Have the ebus connections been made securely? They can be joined anywhere.

Did the installer remove the standard cylinder stat?

The option by default (0) is that only 1 zone valve will work at a time. This priority system is such that when the DHW is selected the boiler will ramp up the flow temp to a higher setting to heat the unistor quicker, then the flow temp will reduce back down to the ch temp set at usually 55/60C.

Your valves seem wired correctly, with the grey and orange not being used.

What is the green neon in the VR65 doing? You will need the cover off to see this.

I have had a VR65 faulty out of the box before and as such always carry a spare as they are so cheap.
Many thanks for further replies.

You (Simon) are right that it just seems complicated! I used to have a Honeywell CM927 so am used to modulating and optimum start firing the boiler at 'funny' times to maintain temperature.


Yes, I know that you have to hold down the 'i' key for 5secs to store a changed diagnostic setting. Confident this isn't the problem with the d70.

ebus connections (boiler and VRC430) are secure, and are joined by terminating together in the VR65 block.

Installer definitely removed cyl stat. I threw it away myself.

Green neon in VR65 is happy, permanently on OK.

Final question: if I currently have the d70 setting at '1' so that both zone valves can open simulataneously, would it be best to change that d70 back '0' (warm water priority) once I turn off the heating for the summer?
I would say yes. I always leave mine on 0 everytime though.

No disrespect, but I have never found the 400 hard to set up or operate. My only complaint is that the instructions are not technical enough.

Just remind me, too lazy to read posts again, what DHW temp have you set as default in the 400?
I assume the VR10 has been wired to the correct terminals, rather than the cyl stat terminals?
Just had another thought. What are the ch and DHW controls (dials) set at on the ecotec? They should both be set at max when using the VRC400 and the VR65. The electronics does the setting of temps automatically.
Yes: VR10 is wired to NTC block in VR65, not 230V stat block.

Cylinder target temp is 60 degrees.

I agree that the VRC 430 isn't hard to set up or operate. It's just that it doesn't quite respond in the way I always expect - based on a week's use! We certainly have plenty of CH warmth and DHW available.

Interesting point: the internal (room) thermometer, I have found, is out by 3 degrees and I have maxed-out the offset to bring it back into line. The external sensor, however, is accurate out of the box. I have checked using a decent probe thermometer from a lab at work.
Yes: both DHW and heating controls on boiler have been set to 'max'.

Perhaps I have been obsessing, and just can't pretend to understand how the software drives it all. As I have said, we certainly have plenty of hot water and heating.

Thanks for advice!
As a long overdue follow up to this topic, I too have a similar occurence (can't call it a problem) but I am using two 2-port zone valves with a VRT360f controller and VR65. With D70 at boiler set to either 1 or 0 (yes I did hold the (i) button for 5 secs until it stoped flashing) the boiler operates with a DHW priority. The CH is programmed to activate ON at 06:30 and the DHW at 07:00.
At 06:30 the CH runs normaly at a steady flow rate of 75C, as set on the boiler as long as the room temperature demand setting of 21C is not achieved. At 07:00, the DHW demand is made by the VRT369f, signified by the flashing tap symbol on the boiler display, and the boiler flame immediately shuts down. After a short pause, the boiler reignites, then cycles quite rapidly until the set DHW temperature is acheived. When checked physically, by feeling leaver positions, the CH valve is definately closed and the DHW valve is open when boiler is cycling. During past summer, when only DHW was activated, boiler operated normally, heating water as required. The system is operating satisfactorily, with cylinder water maintained at correct temperature. Just dont understand why DHW seems to shut down CH despite D70 setting being at 1. and boiler then operating for only short periods (cycling) which it doesn't do when only DHW is activated via VRT360. Worried that cycling will shorten the life of the gas valve etc. What do you make of this situation, if anything?

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