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Vaillant VR66 wiring control centre causing heating modulation woes?

Discussion in 'Plumbing and Central Heating' started by Matthew B, 16 Jan 2021.

  1. Matthew B

    Matthew B

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    For two years now we've been strugging to achieve modulation of our central heating, and I'm starting to wonder whether the VR66 is the problem. Here's our setup:

    vSmart thermostatic controller, connected to...
    VR66 Wiring Control Centre with NTC sensor for hot water cylinder, connected to...
    Vaillant ecoTEC Plus 624 system boiler.

    Our problem is that the boiler has never modulated when running the central heating. It charges the hot water cylinder without any problem, scheduled to do so at the end of the evening when there's no heating demand. However, when there's a central heating demand from the vSmart, the eBUS heating flow temperature being requested (D.009 on the boiler display) is ridiculously high: - we've seen 90°C when it's 1°C outside and the heating curve is set to 0.9 on the vSmart.

    Once the boiler's fired up, the heating flow temperature doesn't change at all, with the result that the room temperature overshoots by 0.6 or 0.7°C. This isn't the modulating behaviour advertised by Vaillant. In the next cycle, when the boiler next fires up, the requested flow temperature may be different from the previous cycle, but it still refuses to modulate, and it's usually above 60°C, even on a mild day.

    We've had our vSmart replaced in an effort to sort out the problem, with no effect. We've done a factory reset on the boiler, again with no effect. We've asked the Vaillant "Controls Champion" whether it could be the VR66 that's at fault, but he reassures us it's a basic switching device, so the problem can't lie there.

    Is there anyone out there with some expertise who could share their thoughts?

    Matthew
     
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  3. rbranco

    rbranco

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    Can you post your D00 setting and also have you checked the D40/41 vs what the actual pipes are at, im just thinking an NTC reading out of spec.
    Can you dial down the max CH flow temp to 65/70c, from what ive read it still acts as the upper limit for the boiler regardless of modulation.
     
  4. Matthew B

    Matthew B

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    Hi.
    I checked when it was on earlier today. Foolishly I didn't check D009, but D040 was 61 (and risìng) degrees and D041 we 49 degrees. D000 is set at a partial load of 16 kW.
    We've manually restricted the CH to 65 degrees, as we hate the radiators getting hotter than that, which also gives a bigger overshoot when it keeps running beyond the target room temperature .
     
  5. rbranco

    rbranco

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    I was under impression that boiler most of the time will not turn off just modulate down, I can see the only way it would turn off is if the temp goes over the max you have set on front on boiler. When it does turn off check the status code on the boiler.
    If it over shoots then maybe your curve in incorrect for property.
     
  6. Matthew B

    Matthew B

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    Hi, yes, that's exactly how the boiler's supposed to work, according to the Vaillant advertising. The boiler is adjusting the flame so that once it reaches the maximum flow temperature we've allowed (65°C), it holds it there until it switches off. However, what's meant to happen next is that the vSmart reduces the flow temperature to maintain the room temperature. It's meant to stop the boiler switching on and off so often, which reduces wear.
    When the boiler switches off, the display shows the standard "egg timer" symbol for anti-cycling. I haven't done any digging deeper into the status codes at that point. Is there anything particular I should look for?
    The vSmart has been adjusting our heating curve setting. It's currently at 1. In the past we've tried adjusting the heating curve manually but it seems to make very little difference in terms of the eBUS request temperatures.
     
  7. rbranco

    rbranco

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    Anti-cycling seems to indicate that the flow temp is going over the max set then it shuts down as it can not modulate down quick enough as there is always a delay between modulation and the flow NTC temp it senses.
    You could lower the D00 setting, ive had to do this on my system to stop it overshooting. I did all the rad calculations and system really only needed 12kw but it was set at 18kw.
    Also have you got TRVs on radiators, I do remember reading a note about TRVs and how they need to be set in the rooms around the controller else you can get them shutting off before the temp is hit etc.
     
  8. Matthew B

    Matthew B

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    We've already turned down the partial load from the original 24 kW to 16 kW. We could try turning it down further and see what happens. I still think it's strange that the eBUS requested flow temperature on D.009 doesn't change at all when the room's near temperature. And whatever the boiler's doing, I can't see any reason why the vSmart would be requesting a CH flow temperature of 90°... Ever! (Especially as the maximum temperature we could ever set on the bioler is 75°C anyway.)
    We have TRVs on most radiators, but not on the radiator in the hall, where the thermostat is located.
     
  9. rbranco

    rbranco

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    Maybe it cant scale back much further, manual seems to indicate a range of 9–24
     
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  11. Matthew B

    Matthew B

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    I think if we took it right down, then the boiler would take a long time to reach the maximum we've set, but so far changing the partial load has had no effect on the flow temperature being requested by the vSmart.
     
  12. Harry Bloomfield

    Harry Bloomfield

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    I get an impression that mine is modulating down as it nears the set room temperature, rather than modulating solely on boiler flow temperature. I have it set to CH 60C, HW 80C (to allow 60C cylinder temperature). I have never known it overshoot on either the room temperature or HW temperature and I record it 24/7 - it just gently brings it to set temperature, whilst winding down the output.

    In warmer weather, when just providing an extra bit of background heat, I have known it not to exceed 35C flow temperature.

    That part at least works absolutely brilliantly.
     
  13. Matthew B

    Matthew B

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    "That's good," he says through gritted teeth!

    Perhaps I expressed myself badly. There are two parts to it. The boiler should adjust the burner to maintain the requested flow temperature from the vSmart, or the maximum we've allowed on the boiler settings, whichever is the lower. That's the part our boiler's managing.

    The other part is to do with the room temperature. Our vSmart control should be doing what yours is doing, and modulating the flow temperature down as the room nears the requested temperature. There's a nice little Vaillant video on YouTube called "How to choose the best thermostat for your Vaillant boiler", and that's exactly what's shown there (starting at 1:33). The flow temperature starts off high and the room temperature rises rapidly until it gets near the setpoint, then the boiler just keeps ticking over to keep it there. It's a lovely straight line on the graph once the room's up to temperature.

    Unlike your system, ours keeps the flow temperature high until the room is just above the requested temperature. Once the boiler switches off, there's still enough heat in the radiators to take it up further, until it gets about 0.7°C above what we've set. The result is a fluctuating temperature, like we'd get with a cheap on-off thermostat, and what we spent a lot of money on the vSmart to avoid.

    I suppose the big question to ask is this: do you have a system boiler, where the vSmart is connected through the VR66 Wiring Control Centre? Or is yours a combi boiler, with the vSmart connected to it directly? I assume it's the system boiler, as you mentioned a cylinder temperature. Also, are you aware of any settings that had to be changed on your boiler to allow heating flow temperature modulation with the vSmart?
     
  14. rbranco

    rbranco

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    I have a VR66 but I am awaiting my VRC720f, ive got a regular boiler so I need HW priority and the module gives me that and also cylstat or NTC connections.
    If you have a system boiler the only reason I can see using the VR66 would be if you needed a trigger to tell the boiler that the cylinder is calling if you are not using an NTC or if you want multizone, but it does say in the manual that VR66 does not support multi-zone with weather comp make sure you have the correct setting 0/1 on the dial inside the VR66 to work as a VR65 monozone else it may disable WC.

    It does not matter how you have your vSmart connected as it eBus is a shared cable, you just chain it.
     
  15. Harry Bloomfield

    Harry Bloomfield

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    Its a heat only boiler...

    Ecofit Pure 18Kw open vented boiler heat only; VR65 E-Bus Control centre; VR10 HW cylinder temperature sensor; VRC 470f Display / control
    VR21 Wireless outdoor temperature sensor; SDM 1901 3-port valve; Grundfos Alpha+ pump.

    None of the settings had to be changed on the boiler, apart from setting 60C for CH and 80C for HW.

    I also programmed the 470F with times and temperatures.

    I installed all of the Vaillant control system and the 3-port. When it was working on the old controls, I could have it share heat between CH & HW, but I was limited to one flow temperature on the boiler.

    The Vaillant system means separate flow temperatures, but it gives priority to HW when the HW needs topping up - so CH can go completely off for 30 minutes, when someone takes a bath.

    The EBus only links the boiler to the VR65, the 470F and outdoor sensors are both wireless.
     
    Last edited: 18 Jan 2021
  16. ScottishGasMan

    ScottishGasMan

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    Mathew B, how old is the boiler? It sounds like an issue with the boiler PCB. Heat curve of 0.9/1 should certainly be producing lower temps than that. From memory a curve of 2.5 gives about 75 degrees at 0⁰c outside.
     
  17. Janko32

    Janko32

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    Hi Matthew B,

    I continued this same conversation on the other topic you started but found you here. I had the same problem as you have until month ago when I just forced heat curve down to unrealistic 0.6 and thats the first time when flow temp reacted to heat curve adjustment (and it lowered flow temperatures down to acceptable values for my house - Croatia / 330m2 / 4 floors / very well insulated / Vaillant Ecotec plus 38 kW / combi boiler meaning HW cylinder / installed late February 2020). I was told by my Vaillant service that vSmart takes 3 months to learn everythiong (as they told him at Vaillant factory on semminars), not just 2 weeks. It takes 2 weeks just to gain basic knowledge of your house.

    Now, iz december after I manually lowered HC to 0.6 it started to work more as it should, meaning no more silly eBus targets at 80-90C. Just for the info I only have radiators, no underfloor heating so 0.6 is unrealistically low. But once the outside temp went to -5-0 the system had hard time reaching the set room temp (dailly 20.5). So I once again manually set my HC to 1 and played with it for some time until I finally set it to 1.2 and with outside temps being as low as -5 it worked perfectly with no overshooting of room temp (only by 0.1-0.2 at most). Just like at your system I never saw that boiler modulates the flow temp down to keep it at flat room temp once it reaches it.

    Now the outside temperatures have gone up to 7-10 C and againg my HC is to high at 1.2 and I think it's not something I should adjust every time the weather changes (gets warmer or colder). Yestedray I hit the automatic button in the app and its now set at 0.9 but I still think flow rises to values that are too high for that curve and outside temp (for example yesterday was 2C outside and the flow was 62 at curve 0.9. Few weeks ago when I thought I have finally resolved my problem at curve 1.2 and outside temp -1 the flow was exactly the same 62C).

    I will continue to monitor whats happening as I have strong feeling something is wrong at both of our systems. Additionally from my experience, once you change the heating curve you should allow the system some time to adapt (lets say min 10 days, preferably 2 weeks).

    Only time I saw the change in flow temp during the cycle is when the outside temp changed (also during the cycle).

    I am still nor sure whether I should call Vaillant to replace eBus and thermostat (still under warranty).
     
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