I am trying to sort out my badly installed woodburner with back boiler
plumbed incorrectly.

Fitting a Dunsley Baker Neutraliser would be very difficult, and as an
alternative I am exploring the use of normally-open motorised valves.

Is there such a thing as a non return valve available for 28mm copper
pipework? I think this would help get a better result. If so, could
someone post a link and/or the proper name for me?

Keith