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Vaillant System Gremlins

Discussion in 'Plumbing and Central Heating' started by rhino707, 23 Mar 2020.

  1. rhino707

    rhino707

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    I fully expect that my lack of knowledge of plumbing and heating systems is the problem here, but I hope someone can help find the issue.

    My heating system is simple single zone open vent setup in a Y-plan configuration consisting of a Vaillant Ecotec Plus 424 with a VR66 wiring centre (setup in monozone/VR65 mode), Vaillant NTC and a single 3 port valve. It originally had the VSmart controller but that was recently replaced by a VRC 700f, by me, as I want to add the Ambisense TRVs (not looking for an opinion on those!).

    The VR66 is wired up in line with the diagrams in the VR66 wiring installation guide (see attached) but I have an issue with the heating. If the room is already above the temperature set in the VRC700 the boiler still fires up and the radiators get warm.

    If I set heating to OFF on the control and let the rads cool down and then set the heating back to AUTO at a time when it is programmed to be on, but with the room temp already above the required temp, the boiler goes through the following sequence:

    1. S.04 Burner on (at the lowest modulation level)
    2. Flow temp rises to 38C
    3. S.07 Heating mode: Pump overrun (5 mins)
    4. S.08 Heating mode: Anti-cycling time (20 mins)
    5. S.00 Heating mode: No heat demanded
    6. Flow temp drops to 32C
    7. S.46 Comfort protection: min load, loss of flame + S.04 Burner on (min modulation)
    8. Flow temp rises to 43C
    9. Go back to number 3 and loop round again and again ....

    The rooms get very warm eventually and I have to set the heating to OFF on the controller to stop the boiler firing up.

    The only thing that I needed to set in the new controller was the system diagram. It indicated an error if I selected anything other than number 1. None of the diagrams seems to correspond to my configuration as they all seem to include VR70/71 wiring centres. The controls brochure states that the controller is compatible with the VR66 in a Y plan config.

    I asked Vaillant which diagram I should select and they just sent me a copy of the Basic Diagram Book that I already had.

    Sorry for the long-winded post but any help for a amateur would be much appreciated.
     

    Attached Files:

    Last edited: 23 Mar 2020
  2. The831Bunny

    The831Bunny

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    There are some fundamental settings that really require the knowledge of the system in front of you. However, as a starting point the following settings are important.

    You can't just plug a VRC700 in and it will work! BTW Ambisence will only work with a VR70 (not a VR66) and an additional VR920 gateway.

    A 700 'should' work with a VR66 with a 424, but depending on your version of VRC700 (1 2 3 or 4) you may need a VR70.

    Set the rotary sector on the VR66 to show 1 in the dial window. Make sure it shows 1 not 0!

    Factory reset the VRC 700 and power down the boiler and VR66 by turning the spur off. Leave off for a minute, power on, then set up the installer menu on the 700. After you have gone through the installation set up, go to the installer menu, password 000.

    In installer settings go to system configuration. Scroll down through the list and change the following settings using the wheel and OK button.

    Adaptive curve to Yes.
    Configure heat circ to Zone 1
    System diagram to 2.
    Type of circuit to Heating
    Set the curve to 2.3.
    Min temp 25C
    Max temp 80C
    Auto off mode Eco
    Room temp modulation to Thermostat.
    Zone 1 assignment to VRC700.
    Cylinder to active.
    HW temp to 60C.
    Parallel charging to Off.
    Max cylinder charging time to 45mins
    Ch pump over run time to 3mins

    Desired temperatures are a personal thing, but 21C and 15C are good starting points.

    See how you get on.
     
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  4. rhino707

    rhino707

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    Thanks for your extremely helpful information. The problem was caused by the Room Temp Modulation being set to none. Pretty dumb mistake I guess!

    It isn't happy with anything but a System Diagram of 1 though. It generates a fault if I select 2, which seems like it should be the correct one, particularly as 1 seems to relate to having a combi boiler.

    In any case, it appears to be working OK now, so thanks again.

    If/when I get around to investing in the Ambisense TRVs, is it a straightforward swap over from a VR66 to a VR70 or is that definitely a job that should be left to a pro?
     
  5. The831Bunny

    The831Bunny

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    Systems 1 and 2 are HW with a single heating zone. If 1 works fine, then that will be the slight incompatibility of the VR66. The VRC700 and VR70 launched together. The VR70 replaced the VR66. The VR66 has ‘previous’ logic, so is not 100% backward compatible. I’ve never fitted a VR66 with a VRC700 nor seen one in the field. Just got the info they don’t speak to each other very well lol!

    Replacing the VR66 with a VR70 is straight forward. Only an extra ebus wire to run the 920 gateway for ambisense. It is physically bigger though.
     
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