An update:
Grant Technical Services emailed me back to confirm that there would be no problem feeding both coils in their DuoWave Indirect unvented Solar cylinder from the same heat source (i.e. a boiler). I must admit I was pleasantly surprised to get a reply as it wasnt a trade enquiry...
Alec1, thanks for the quick response, this is reassuring to know. The Vaillant controller (VRC 470) has an NTC sensor (VR10) that fits in a dry pocket in the cylinder so it can accurately monitor the actual vs target temperature of the water in the cylinder so I would hope that this should help...
This is my first post in this forum, but I have been lurking here for a couple of years as have previously found it to be a mine of useful information.
My current system comprises a Vaillant ecoTec 637 (37kw) boiler with Vaillant eBus controls (VRC 470, VR61 2 zone centre, VR81) and a vented...