I have an old Potterton boiler with gravity hot water and pumped heating.
The system still works very well and seems reasonably efficient (£25 monthly
for a 4 bed detached). However, during the colder months, I have far too
much hot water at too high a temperature. Would it be possible to add a
thermostatically controlled valve to the return from the hot water cylinder
(thus maintaining the vent on the flow pipe) in order to control the hot
water temperature. I have a 3-way motorised valve which I could use by
blanking one of the inlets, and then controlling it from a cylinder stat.
Would I also need a narrow bore by-pass.

Terry D.