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Discuss Vaillant wireless VRT 392f ebus control modulating advantages? in the Central Heating Forum area at

  1. John Mathews

    John Mathews New Member

    Some info about interaction of Vaillant wireless controllers with the Vaillant ebus system please. Does connecting the wireless receiver to the ebus effect the boiler modulation and if it does what is the benefit over a simple on/off thermostat? I have had problems over the years with this system disconnecting and not reconnecting so am considering other options.
    Replace with Honeywell, Nest whatever - will I be missing out by not having to access the ebus?
  2. Brambles

    Brambles Member

    The Ebus is an Open Therm (OT) type of gateway that does not use the OT protocol. To operate the boiler ( adjusting the modulation externally) Ebus needs to be matched with an appropriate Vaillent controller. There are interfaces available (VR33, I think) that can be used to interface an Open Term controller to Ebus.

    My advice: if using Ebus match it with an appropriate Vaillent controller.

    With respect to Open Term type systems (they all have their peculiarities) they can be very effective - but it very much depends on the boiler and it’s suitability to the controller. My experience is mainly with Evohome, but we do get some challenges. Sometimes a good boiler performs better (and often more predictably) with a simple on off control rather than Open Term where the decisions are made by a third party (ie Honeywell) controller.

    On a final point, if you are looking for the control system ( either simple or Open Therm style systems) to save money - look hard at the equipment and interface costs. For Evohome moving from simple to OT control adds around £100 to the cost of what ( in my view) is a bery good system - but expensive.
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  3. John Mathews

    John Mathews New Member

    Many thanks. I think there must be a bug within the Vaillant system that causes the wireless system to not only disconnect but then not reconnect. In my case it occurs about twice, maybe three times a year, at which point the house can reach 30 degrees mid winter (the manual instructs that the boiler temperature control be set to max). Vaillant suggest moving the wireless receiver away from the boiler which indicates that the signal is weak or else there is interference from the boiler. Is there any specific information about how or why such an rare, intermittent fault is happening. If the signal is weak or there is interference from the boiler I would expect more regular failures. By the way the boiler is in a cupboard with a painted MFD door. I have had the metal cover removed from the bottom of the boiler. The thermostat is next to the door in the front room, downstairs and the boiler is in the backroom, downstairs. Just two doors including the cupboard between them and total distance is about 5 metres. Right now everything is working fine. When the fault occurs, I turn off the boiler, turn it back on, press the button on the receiver and eventually it starts working as normal
    Last edited: May 17, 2019 at 11:02 AM
  4. OffshoreGas

    OffshoreGas Top Contributor!!

    It may be worth a call to valiant to ask if a firmware upgrade exists for your controller. Although Zigbee has been about for years heating manufacturers haven’t been using it for that long. In their defence hard to test in a development environment all possible scenarios.​

    In theory at least there are big advantages in terms of reliability and economy to utilise modulation in boiler control.

    With on/off control the heating is on or off, it’s equivalent to driving your car by either having the throttle either off or flat to the floor. As you can imagine constantly heating/cooling a system like this doesn’t do it a lot of good, also lots of mechanical bits like valve are moving more than they need to.

    Modulation tried to match the heat output to the conditions. This is achieved by running At say 15% capacity constantly for a much longer period.

    Obviously the boiler manufacturers want to sell you controls as well as just a boiler so there may not be as much cooperation with Nest/Honeywell as you’d like to think. The other advantage of sticking with one make is it avoids finger pointing with any issues now or at a later date.
  5. Brambles

    Brambles Member

    Vaillant uses 868MHz to connect wireless. Good practice would be to have the two wireless receivers / senders 600mm away from any solid lump of metal and not within 600mm away from any other wireless device or microwave oven.

    I don’t think that the system works on just receiving one signal. There is a verification protocol. Unfortunately, to diagnose the problem you really need to be able to read the interface to understand the instructions being sent. That is not straightforward on the Vaillient system - unless you are into Raspberry Pi’s!

    I would try relocating the controllers - if that is ineffective, look at switching the control system to Evohome, but not operating on Open Therm.

    If you want more detail on this type of issue look at the Automated Home Forum - search for Evohome. You will see a number of threads relating to interfacing with Open Therm / Ebus systems - and the vagaries of different manufacturers

    Hope this helps
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