Unable to set 'cylinder boost' for extra HW on Vaillant VRT350F

[DRSB]

Hi all, newbie here. Less than a year ago I had a new Vaillant Ecotec boiler installed with a VFT350F controller. It connects via a VR65 control box to my existing honeywell gravity fed cylinder. It works well when programmed to come on, but I have never been able to get the 'cylinder boost' function to work when I want an extra hour of hot water, which I now realise is because there was no VR10 NTC installed.

I installed one of these today on the return pipe and wired it to NTC connector in the the VR65, initially leaving the cylinder thermostat in place set at 70C as a back-up. The VRT350 now shows the cylinder temperature and will let me activate cylinder boost mode but unfortunately it won't let me change the desired cylinder temperature (just flashes). This means when cylinder boost is activated it reads 'desired temp 5.0 C' (and therefore doesn't actually turn the boiler on as the temp is about 30). I have also tried moving the VR10 to the space where the old honeywell thermostat was (in a space in the foam) and also disconnecting the thermostat from the VR65 but this makes no difference. Any ideas would be gratefully received - it's driving me mad!

Thanks,

 

[DRSB]

I took some photos if that helps:


This flashes constantly when trying to adjust and won't accept any changes, although when I go into the installer menu it seems to let me adjust it there (and works when the programmer comes on).


During cylinder boost it is fixed at 5 degrees which I assume is why it doesn't work - I can't find where that is set?!

 

[Steelmasons]

What is the hot water temp on boiler set too?

 

[DRSB]

When I go through the installer menu I have it set to 60C at the moment. I don't think the connection with the VR10 is quite as good as it was with the original thermostat as it was set on 60 before with that but the cylinder/water not as hot.

And on the actual boiler it's et to 65