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Thread: Vaillant flow temperature control for HW

  1. #11
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    That'd be great. TYVM

  2. #12
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    Quote Originally Posted by fezster View Post
    That'd be great. TYVM
    Just checking if anyone has found the answer to this? I have a Vaillant VR66 unit that provides a DHW signal to a Vaillant boiler via the ebus. It seems that the VR66 does not set the DHW temp, and the max I can set the temp via the boiler is a measly 65C. This is no good, I was hoping to get about 75.

  3. #13
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    Quote Originally Posted by Symbolics View Post
    Just checking if anyone has found the answer to this? I have a Vaillant VR66 unit that provides a DHW signal to a Vaillant boiler via the ebus. It seems that the VR66 does not set the DHW temp, and the max I can set the temp via the boiler is a measly 65C. This is no good, I was hoping to get about 75.
    The 65oc is the temperature of the water not the flow temperature, not sure why anyone would want it any hotter than this? I find 55oc too hot at the taps.

  4. #14
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    Quote Originally Posted by mtmcgavock View Post
    The 65oc is the temperature of the water not the flow temperature, not sure why anyone would want it any hotter than this? I find 55oc too hot at the taps.
    My Vaillant is not a combination boiler.

    I am using the Vaillant system to produce hot water to circulate in a Megaflo tank. I would like to keep the Megaflo at 60 degrees, to prevent Legionella. To achieve this efficiently I need to generate hot water using the Vaillant that is at 75 degrees, which is circulated inside the Megaflo and radiates its heat into the Megaflo.

    If the Vaillant really as an arbitrary max of 65 degrees, then I might stop using the Vaillant for how water and re-deploy it as a secondary central heating boiler, and get a very simple boiler for hot water generation that has a simple dial on the front for setting the flow temperature.

  5. #15
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    Quote Originally Posted by Symbolics View Post
    My Vaillant is not a combination boiler.

    I am using the Vaillant system to produce hot water to circulate in a Megaflo tank. I would like to keep the Megaflo at 60 degrees, to prevent Legionella. To achieve this efficiently I need to generate hot water using the Vaillant that is at 75 degrees, which is circulated inside the Megaflo and radiates its heat into the Megaflo.

    If the Vaillant really as an arbitrary max of 65 degrees, then I might stop using the Vaillant for how water and re-deploy it as a secondary central heating boiler, and get a very simple boiler for hot water generation that has a simple dial on the front for setting the flow temperature.
    You are mis understanding. The 65oc is the temperature of the water in the cylinder. When using the VR66 you have to use the Vaillant NTC probe into the cylinder. This then measures the temperature of the HW, which you set in your Vaillant controller, or on the front of the boiler. You then set which flow temperature you require for heating DHW in the Diagnostic menu along with what KW output you require for the cylinder.

    Settings D.020, D.077 and D.078 is what you require.
    Last edited by mtmcgavock; 3rd February 2019 at 06:09 PM.

  6. #16
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    Quote Originally Posted by mtmcgavock View Post
    You are mis understanding. The 65oc is the temperature of the water in the cylinder. When using the VR66 you have to use the Vaillant NTC probe into the cylinder. This then measures the temperature of the HW, which you set in your Vaillant controller, or on the front of the boiler. You then set which flow temperature you require for heating DHW in the Diagnostic menu along with what KW output you require for the cylinder.

    Settings D.020, D.077 and D.078 is what you require.
    Sorry, yes I did understand that using the NTC probe was one way to go. But I thought that the VR66 can alternatively take, as its input, the cylinder temperature dry contact that simply signals a demand for more hot water generation. This is the operating mode I am using. The primary benefit of this operating mode is that it allows me to site the Megaflo tank in the middle of the house, and the Vaillant boiler about 20 metres away in a boiler house. This keeps the noise levels down. Obviously the hot water has to travel over than 20 metres with very little heat loss - which it does, in my set up. I have Uponor district heating style insulated underground pipes and I lose less than one degree over that 20 metres.

  7. #17
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    Quote Originally Posted by Symbolics View Post
    Sorry, yes I did understand that using the NTC probe was one way to go. But I thought that the VR66 can alternatively take, as its input, the cylinder temperature dry contact that simply signals a demand for more hot water generation. This is the operating mode I am using. The primary benefit of this operating mode is that it allows me to site the Megaflo tank in the middle of the house, and the Vaillant boiler about 20 metres away in a boiler house. This keeps the noise levels down. Obviously the hot water has to travel over than 20 metres with very little heat loss - which it does, in my set up. I have Uponor district heating style insulated underground pipes and I lose less than one degree over that 20 metres.
    Even when using the standard Stat on the VR66 the flow temperature will revert to the D.078 setting. The Hot water setting on the boiler stays active as it's a software limit, even when just using a Switch Live rather than a VR66 it's still adjustable.

  8. #18
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    Quote Originally Posted by mtmcgavock View Post
    Even when using the standard Stat on the VR66 the flow temperature will revert to the D.078 setting. The Hot water setting on the boiler stays active as it's a software limit, even when just using a Switch Live rather than a VR66 it's still adjustable.
    Yes, I have D.078 set at 80 degrees. Regardless, what happens when there is heating demand is that the boiler goes to about 65 degrees on the flow temp, and then goes into pump overrun mode. So even when there is no NTC connected allowing the boiler to figure out what the cylinder temperature is, the output DHW is modulated down to 65, and the actual temperature varies between 60 and 65.

    It is also interesting that the boiler seems to look at the return temperature and set a flow temperature based on the incoming water temperature. If the return temperature is (say) 52 degrees, the flow will be about 60. Maybe this is to allow condensing to happen, but in this mode the boiler is modulating right down to 8kW. This causes a very slow heating of the cylinder, which in turn causes long run times for heating mode.

    All in all, far from ideal, and I regret using the Vaillant boiler for this application. I may still buy a dedicated DHW boiler with a simple DHW temperature control that can just heat the water to the commanded temperature without too much additional undocumented “smart” behaviour getting in the way.

  9. #19
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    I don't know if this might help...

    Vaillant ECOfit Pure 418, VR 65 Control Module & VR10 cylinder sensor, VRC 407F Controller + VR 21 Outdoor sensor + Radio Receiver in boiler + Sunvic SDM 1901 3-port

    In a fully open vented system. With just basic clock, mechanical stats for controls, the boiler only allowed one temperature output of 60C (I think). I added the above Vaillant controls and can now set separate output temperatures for HW and CH, up to 80C. On CH the controls decide how hot the flow needs to be for CH, which usually means it stays below the maximum condensing operation temperature most of the time. It also now modulates it output much better than before, avoiding the on full/ completely off of the older system. Much less creaking of pipes as they expand and contract.
    Last edited by harrym1byt; 4th February 2019 at 10:22 AM.

  10. #20
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    Quote Originally Posted by Symbolics View Post
    Yes, I have D.078 set at 80 degrees. Regardless, what happens when there is heating demand is that the boiler goes to about 65 degrees on the flow temp, and then goes into pump overrun mode. So even when there is no NTC connected allowing the boiler to figure out what the cylinder temperature is, the output DHW is modulated down to 65, and the actual temperature varies between 60 and 65.

    It is also interesting that the boiler seems to look at the return temperature and set a flow temperature based on the incoming water temperature. If the return temperature is (say) 52 degrees, the flow will be about 60. Maybe this is to allow condensing to happen, but in this mode the boiler is modulating right down to 8kW. This causes a very slow heating of the cylinder, which in turn causes long run times for heating mode.

    All in all, far from ideal, and I regret using the Vaillant boiler for this application. I may still buy a dedicated DHW boiler with a simple DHW temperature control that can just heat the water to the commanded temperature without too much additional undocumented “smart” behaviour getting in the way.
    To me it sounds like you've got some form of circulation issue on the cylinder circuit, at a guess it sounds like it is returning too quickly or your pump is on it's way out. It's not a problem with the VR66 or the boiler setting at 65oc.

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