CWST back filling up cold feed

[Frazer1981]

Hi

Just looking for some advice.

Have an indirect cylinder, open vent htg and hw.

When the customer turns the heating on the small header tank starts trying to fill and the cold water storage tank starts to back fill up the cold feed. How water is also really hot coming out the hot taps. My gut feeling is this could be an issue with the cylinder coil but just wondering if anyome has advice!

Any help much appreciated

 

[Riley]

Sounds like a split coil. Which loft tank is higher

 

[Frazer1981]

Sounds like a split coil. Which loft tank is higher

Both sitting on the joists but the CWS is higher and a bigger tank