I currently have a simple sealed, pumped heating system with one zone,
a timer control for the boiler and TRVs on all the radiators. However,
the hot water cylinder is electric only via the immersion, and a long
way from the boiler.

I recently replaced the cylinder, and with foresight installed an
indirect one. I now have an opportunity to run a connection to heat the
HW from the boiler somehow - but routing the pipework is tricky!

The easiest solution appears to be to treat the HWC as just another
radiator, and tee it into the existing circuit just before the final
radiator (which is the closest one). Is this a possible/sensible
solution - how could I control the HW temperature? Or am I going to
have to bite the bullet and find some way of running a new zone all
the way back to the boiler?

Vaci