+1 If you implement the planning permission expect to have to pay the S106 agreement.
You should get a copy of the planning permission and S106 agreement from planning.
I think it should be possible to have standard single wall black flue pipe into the chimney.
Hetas installers will check the chimney is suitable for solid fuel.
With some mixers if you accidentally connect them incorrectly they won't work at all, with others you can just swap the internals around, no need to re plumb. Check your new one.
Some of this is down to the supplier. Will they give your PM his normal discount if the order isn't going through his account? If it is going through his account then you will probably have issues with the reclaim.
Chances are we are only talking about a few builders merchants. Why not ask your PM if he can help you get an account at the BM, possibly with a similar discount ?
I need to replace two sealed units in wood frames. The windows have internal beads not external putty thank goodness.
So would you recommend glazing tape or low modulus silicone to seal the glass into the frame? Both? This will be the external water seal.