Failing hot water

Have diagnosed the problem as the input from the header tank is blocked, well thats what the man from BG said after second visit and replacing PCB pump etc... he suggested that I have a new header tank fitted and feed the thermal store via the return pipe!

Spoke to someone at Gledhill today and he suggested this was not the way to fix that problem, and the correct way was to drain both tanks fit a something connector to the drain and drill the tank half way up fit another connector and join the two use this as the new input. He also suggested any local plumber could do this?

I live in North Bristol and some of my neighbors are suffering with the same problems... Can someone suggest 1. a reputable plumber 2. an estimate of how much this would cost?

It takes about an hour to fit one of these external fill pipes, and £15 in materials. Two hours for a plumber doing it for the first time.

I can come to Bristol if you like, but I charge for travelling time as well as time on site.

Cheers, Mike