Vaillant Ambisense

12 Aug 2009
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United Kingdom
I have the following setup which I cannot get to work as it should? when I turn up the temp on one of the VR50 TRV's the boiler does not fire up!
I suspect that the VRC700 settings are conflicting with the Ambisense TRV's / VRC App?

Vaillant 831 Ecotecplus boiler
VRC 700 programmer installed in the boiler facia
VRC920 Ambisense controller connected via ebus cable to the boiler.
VR50 Ambisense TRV's
VRC iPhone App

I know the TRV's are getting a signal as when I change the room temp on the app, it displays in the TRV and I can hear the valve motor running.

Any ideas on where I'm going wrong would be appreciated.
It looks so easy on the Vaillant web site and videos(n)
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Daft question, but is the heating turned on? If the room temperature is higher than the trv, it shouldn’t come on anyway.
Yes, the heating is on. If I turn up the TRV's in the living room to a higher temp than the actual room temp, the boiler does not fire up.
I suspect it's one of the settings in the VRC700 over riding the TRV but I don't know which one(n)
I forgot to say earlier that I don't have any time settings in the VRC700 program controller as it's all done with the VRC700 Ambisense App.
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Summer mode active? Just a guess.

Edit... Do you have to leave the original controller CH to always on? Or is there a link that needs to be removed?
Last edited:
Vaillant tech help have said leave the VRC700 on 'Auto' but there is mention in a manual of leaving setting as 'Heating On' I have tried both settings and no difference, can't get boiler to fire up when TRV temp increased.
Vaillant seem to think the EBus connection is not working but I'm sure it is as my phone app tells me the hot water temp setting, CH flow temp. the App also tells you that everything is working, no faults ?
Still trying to get this setup working. Just set the VRC700 to default and restarted the VR920. When setting up the VRC700 it goes through various screens one being a screen message that it's searching for Ebus components.
When complete, it lists two devices: "Control" and "heating device"
Does anyone know if "control" is the VRC700 or the "VR920" ? or should there be 3 devices listed?
Is the 24V link in the boiler?
Is the heating temperature turned up to max at the boiler?
What is the summer offset set to on the 700?
Was the system installed and commissioned by a heating professional?
The VRC700 is plugged into the boiler Facia (Ecotecplus 831), the dial on the boiler is set to max as recommended for the weather compensator.
There is no offset set for the summer setting.
It was installed by myself, The Vaillant into makes it sound so simple!
I have just come home from work and the two radiators without VR50 TRV's are hot!
The 700 is a complex controller for gas and oil boilers, solar, air and ground source heat pumps and multi-zoned systems. To commission it properly you do need a knowledge of heating system design.

VR50’s are designed to be fitted to all TRVs in a property. When operating correctly and there is a demand from a VR50, the VRC700 will display ‘day’ mode. If you alter it to auto, it will return to ‘day’ mode within 15mins. All timings and temperatures are handled in the app. If there are rads without VR50’s, they will turn on when the boiler fires for heating.

Check the correct system is set in the 700. It should be 1 for a combi. The 700 if installed in the boiler fascia should be set to ‘none’ in room temp modulation.

It’s also not impossible that you have a diverter valve problem within the boiler causing your rads to heat when pre-heat or HW is operating.

Other than that, check for high set back temperatures, time and date incorrect, anti- legionella set to operate (not needed on a combi), poor connection on the ebus from the 920, the 920 losing internet connection.
I checked the settings:
VRC700 is in Auto mode (Sun sign on screen under the word Auto)
Heating is set as Zone 1
room temp modulation - none
anti Legionella - off
set back temp - 12 deg

The TRV's are receiving a signal, if I request a higher temp than what is set in the App, it appears on the TRV display.

The app also shows me the temp setting for the DHW, the CH pressure and the flow temp from the boiler.

If I ramp up the temp to 30deg on one of the TRV's, should this not make the boiler fire up as at the moment nothing happens at the boiler?
Depends on the outside temperature. What is your outside sensor reading? If the summer offset is set to 0 it means at an inside temperature of 21C and an outside temperature of 21C the heating is off. As it’s warm, adjust this to temporarily test the system. Make sure the system diagram is set to 1. A demand on the ambisense will trigger the boiler, but there are so many more variables that may be preventing it coming on. Press the I button on the boiler or look in the 700 information to check the status of the system. Does the temperature changes show in the app ok?
Hi, sorry about the delay in getting back to you.
The system diagram is set to 1.
The current outside temp is 17.5 as shown on the app.
At this moment, the heating is on, the radiators without VR50's are hot except one radiator with a VR50 is hot although it is set to auto in the App. The temp is set to 18deg and the room temp is currently 26deg. Could there be some fault in this TRV?
If I change the temp in the App for a particular radiator, it does change on the TRV display.
If I press the 'I' on the boiler panel I get the following:
5.0 42deg
Heating symbol, C, pump symbol pump

Does the setting "Desired Temperature" displayed on the VRC700 controller have any influence on things?
S.0 means the target flow temperature is above the flow temperature requested from ambisense. So it’s come on, reached the flow temperature and then turned off. If the radiator symbol is on the boiler display, there is a heating request from the controls. A heating request is in the form of a temperature the controls calculate to be circulated around the radiator(s). This is calculated from your ‘desired temperature’, the actual room temperature measured from a VR50, and the actual outside temperature from the external sensor.

The desired temperature on the 700 display is the highest room temperature requested from any/all of the VR50 heads.

You could have a faulty head. Double check in the app per room if you have any rogue temperatures. But you definitely have a demand there.

As a guide, ‘on’ room temperatures are 21-22C, ‘off’ or setback temperatures are a whole discussion, but if you live in a reasonably insulated house, then 16C is fine. Bear in mind the VR50 head may very well send a flow temperature request of 25-35C as the room temperature drops and approaches the ‘off’ or setback temperature. If this is undesirable, set the setback temperature lower.

If you turn the heating to summer/absence mode in the app (Check radiator symbol has gone and S code is S.31 at boiler, and you still have warm radiators, you have a diverter valve problem in the boiler.

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