Vaillant controls compatibility issue -perhaps

30 Dec 2018
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Up North
United Kingdom
This was the system at the start of last week and all working fine..

Open vented boiler and HW cylinder with a Vaillant ECOTec 418 Pure boiler (installed last March) + a basic timer + mechanical stats + Sunvic SDM 1901 valve/actuator. That setup meant there was only one setting for boiler flow temperature, which I had set to75C to get the HW cylinder good and hot. 75C meant the boiler tended to run near flat out, or off, when heating for the CH too, with little modulation down.

During the week, I upgraded that by removing stats + timer and installing a VR 65 Control Centre + VRC 470F, including wireless outdoor sensor. CH works great, modulating boiler up and down nicely, but I am obviously still tweaking the Heat Curve value.. (That is apart from Problem 2).

Problem 1 Idea was to be able to split the boiler output to be able to have higher temperature for HW, than needed for CH and run CH in condensing mode. It has enabled split, but the max setting for HW at the boiler is 60C and 75C for CH. The 470F allows the HW desired temperature to be set at a max of 70C. At 60C from the boiler, the cylinder struggles to be got higher than 50C, so demand is never met.

Problem 2 When HW is demanded, it seems to circulate to the CH circuit too. Thinking I might be able to get the water hotter once per day, using the anti-Legionaire facility, I set that up as a test today. Boiler ran very hot (85C) and it did raise the HW from 50C a couple of degrees, but it also got the CH hot too, stiflingly so. The SDM 1901 seemed to be regularly cycling between HW and CH, despite no CH demand. I never actually spotted it in mid-position at all.

I also tried configuring the boiler to use a mid-position valve d.97 to option 1.

Despite the warning to only use a NTC sensor on a uniSTOR cylinder, I tried both my original bi-metal stat and swapping to the NTC to see if that made a difference - it didn't.

Your suggestions please gentlemen?

Is the VR65 Control Centre perhaps incompatible with the SDM 1901?

I emailed Vaillant three times, in my attempts to get their assurance of compatibility of these items before purchase. Three times they ignored my question, only suggesting that VR66 and VRC 700 were the latest models.

Finally, how can I tell whether the 470F has a DCF77 receiver or not and whether it is receiving? Oddly this morning the clock and date (correct yesterday), had changed to 23:00 and 05/05/19 at 08:30 20/01/19. I wondered if it might have received corrupted data from DCF77, though odd if it just accepted it with checking the check-sum..
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The sunvic 1901 is a momo valve so fairly sure its not compatable with the vr65, change the complete valve for a Honeywell 3 port.
I did wonder if that might be the case - The 1901 momo was swapped for a the originalled installed 2701 spring return 3-port and is electrically compatible with the 2701. My idea in the swap, was because I found the 2701 very unreliable. Vaillant give no other clues in the VR65 instructions about the actuator compatibility, other that it can use 2x 2-ports or 1x 3-port.
So, next questions - has anyone found a method to make an SDM 1901 appear to a VR65 as an Honeywell actuator?

Which Honeywell models does the VR65 actually work with please?
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Just managed to ring Vaillant's trade tech.. They suggest the VR65 is compatible with ALL 3-port valves, though I am still not absolutely convinced so I swapped the actuator for a second good Sunvic SDM 1901. It Sunvic unit 2 misbehaved exactly as Sunvic 1 and both perform exactly as they should on a bench test.

Regarding 'problem 1' the HW set temperature. The HW setting on the boiler, only appeared as an option when I fitted the VR65, with a max setting of 60C and as before 75C for CH. Vaillant said to just ignore the setting on the boiler, what applies is the setting in the VRC 740F, that the HW setting in the boiler only applies to when it is a combi boiler, not a system boiler..

Anyone able to confirm whether or not there might be some electrical difference between the Sunvic SDM 1901 and other actuators please, particularly the Honeywell units?

Sunvic SDM 1901 works as below..

Blue = Neutral
Make orange live = HW Only
Make White + Grey live = CH Only
Make White + Orange live = mid position HW + CH
There are two mid positions.

Orange live signals boiler/pump to run. Actuator is a momo, only rotating in a single direction under motor power until it achieves position.
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This is absolutely doing my head in, trying to get to the bottom of this HW heating issue....

When HW is called for - sometimes the 1901 moves to the HW position, then despite heat being needed the boiler fails to light up, sometimes it does light up. Vaillant assure me that the VR65 is designed to work with ALL 3-port valve actuators. I have test 2x known good actuators, both misbehave on the VR65.

The VRC 470F, going into Installer Level> System> Control Modules -List, shows Display 1.24; Receiver 1.20; VR61 1.15; Heat Generator 7.02...

I would have expected the VR61 to be VR65 - What I fitted was a VR65 and a VRC 470F... VR65 came in a box marked VR65, the manuals matched the contents and the VR61 is a very different animal..
There is a plug available for the 400 series ecotecs to allow the ntc to be connected directly to the boiler pcb, do a search for mrv as he has posted about this issue.
There is a plug available for the 400 series ecotecs to allow the ntc to be connected directly to the boiler pcb, do a search for mrv as he has posted about this issue.

I don't understand relevance to the issue...

A VR10 came with the kit, installing it in the dry pocket intended for the immersion heater stat. and connecting it to the VR65, the VRC4070F shows the cylinder temperature correctly. Even so I can see there ought to be a call for HW heating on time / temperature, or a boost request, the system responds apparently randomly. Sometimes it moves the 3-port valve correctly to the HW position, sometimes not, sometimes even when the valve is correctly positioned, the boiler fails to be triggered. Even when the boiler is triggered, there is then no certainty that it not shut down long before the cylinder is heated to the desired temperature. A couple of times, the boiler has fired up at close to maximum temp/output, as if it was about to heat the HW cylinder

So basically HW is very random. I have tried running it from the NTC or the bi-metal cylinder stat. the system behaves the same on both. I have swapped the known good Sunvic SDM 1901 actuator for an second identical known good actuator, that made no difference.

Trying a Legionella cycle it seemed to try to heat the cyclinder, but instead heated the radiators.

The CH alone works exactly as it should, perfectly. The only issue is the HW heating side.

Vaillant insist the VR65 is compatible with ALL 3- port valves, including my Sunvic. Vaillant say the HW max setting on the boiler is not relevant to a system boiler, all that matters is the desired HW temperature set in the 470F (max 75C).

My system (installed by me) worked absolutely fine on its old controls, until I swapped it out for the VRC 470F + VR65. Both items were bought as new, unused items, old stock and were obviously untouched.

I am a retired electrical/electronics engineer / control systems specialist, well used to getting complex systems right first time and have repeatedly checked this basically simple setup and can find no fault. My best guess at the moment is there is an issue with the VR65.
Thanks, but I still don't understand the relevance to my HW issue.

I already have an out door wireless temperature sensor (VR21), that feeds data to the system so it can select its proper central heating curve. The cylinder has a VR10 NTC temperature sensor in the cylinder, for controlling the HW temperature. Both are feeding proper data to the VRC470F wireless display/ control. The VR10 NTC was included with the VR65 kit.

The boiler does have a socket for a wired NTC outdoor temperature sensor, but that is already provided to it wirelessly by a VR21.

The VRC470F is also wireless, linking to a plug in to the boiler unit, which is part of the the 470F kit.
I have done a factory reset on the ECOtec boiler and it seems to have done the trick, or at least one test call for HW has worked to produce its first tank of HW :)

My assumption when I installed the VR65 and VRC470f, was that all I needed to do was power the whole system down, install and power it back up.

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