Has anyone used a Viessmann Vitodens 100 with the Combi add on to heat domestic water in a storage tank? Think Aquastat, stainless or bronze pump, and relay that turns pump on and forces flow into the unit setting off the flow switch which turns on the boiler o heat the plate exchanger to heat domestic water and when the tank is satisfied (aka Aquastat) pump shuts off? Sorry, I just can't get past short cycling the burner, but I think this would probably be a great way to produce DHW without short cycling the burner, especially if you had an Aquastat with adjustable differentials, etc.
I was then also thinking if you use an indirect (perhaps a Vitocell 300) as your storage tank for the above mentioned set up, you could use the indirect coil for solar DHW heating. This would be one way to integrate the Viessmann 100 Vitodens Combi with solar/storage tank. Just a thought anyways.
Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber
I think it will be possible but very expensive to build and run. You will need very powerful circulator to work against resistance of heat exchanger. HX designed to work on street pressure and for 4 GPM might require over 30' of head of a pump. Pump must be SS or bronze. And electric bill will be very high.