EvoHome, VR33 OpenTherm w/ Vaillant Ecotec VU

[CharlesNote]

I have a Vaillant Ecotec VU 656/4 installed in 2017 an EvoHome Control System (Cylinder Stat, Rad valves) on an S-Plan System with BDR91 connecting to the HW and CH valves.

The boiler is operating in on/off mode connected via the 230v Terminal 3 and 4.

To try to take advantage of the boiler modulation, I have installed the VR33 module, wired to the OpenTherm Bridge (R8810A) connected to the EvoHome system.

I have placed jumpers between Terminals 3 and 4, as well as the 24V RT terminal 7 and 8.

The system recognises the VR33/OpentTherm control: D.90 = 1

However, the boiler stays in S.31: No heat requirement from eBUS controller (D.23 = 1 Heating on i.e. not summer mode), even though the system is calling for heating and/or hot water with valves open.

The VR33 installation instructions are not clear, but the green status LED on the VR33 board flashes (blips) every second. I'm unsure whether this is Flashes: Normal Function or Flashes Rapidly: No eBUS connection to the heat generator.

Has anyone come across this before and managed to resolve?

Thanks.

[bruce_miranda]

Try this. Instead of the R8810A connected to the VR33, just use a jumper wire. The boiler should fire with the VR33 pins shorted.
D.9 should go to 90C when you short the pins of the VR33..And when removed it should go to 10C.

[CharlesNote]

Thanks for the guidance.

Yes, shorting the VR33 fires up the boiler, D.9 displays 127C and the VR33 LED flashes regularly.

D.9 displays 10C without the jumper.

Does this suggest a problem with the R8810A module itself? The Evohome binds with the module without a problem and I get the green led flash every 10 seconds.

[bruce_miranda]

What does D.9 show with the R8810A module connected and Evohome calling for HW?

What does D.9 show with some CH demand, confirm that Evohome is definitely seeking demand.

[CharlesNote]

D.9 shows 10C when there is either HW or CH demand with the R8810A attached.

On the evohome display, the Opentherm is being shown as open along with the relevant HW or CH valve, but boiler doesn't fire up and status code stays as S.31: no heat demand. Also the VR33 LED doesn't flash regularly like when the jumper was placed on the VR33, which suggest no ebus connection.

[bruce_miranda]

What does the Demand % show in the System Summary screen for when HW or CH is ON

Are you getting a regular blink from the R8810A LED when connected?

[CharlesNote]

For HW 100%. For CH depends on temp difference between current and target, for smaller difference it was 80% matching the HR92 radiator valve %.

Regular 10s green LED blink on R8810A.

[bruce_miranda]

Reset the binding on the R8810A and bind it again and try. If that doesn't work, then I think the R8810A is at fault.