Water hammer can be a tricky thing to cure.
Personally I have had varying degrees of success.
I find shock arrestors don't work. The same with turning down the internal stop tap.
What I've found is turning the the external stop tap down a good few turns can be a cure.
Hope this...
There are rules as to where any flue is positioned because it's not only steam its products of combustion. If it's a nuisance to you then a call to Gas safe for their advice would be a sensible approach.
Your neighbours sound like a nice family. Not.
Andy...
If your pressure is dropping either you have a leak somewhere or the pressure relief valve is passing. Start with the radiator valves feeling at the back and tie a plastic bag over the prv to see if it's passing.
Andy
How about re piping from the nearest accessible place either side of the pump and bypass it altogether fitting your new pump in a better position.
Andy.
Those nuts don't usually need anything on them to make the seal as long as both faces are clean and not damaged. I'm wondering if the leak is where the tail (with the hex shape inside) is screwed in tightly enough. This tail should have Ptfe tape on or preferably loctite 55.
Andy.
If you are in a smoke control area and are planning on burning wood which isn't a smokeless fuel you will need to fit a defra exempt stove.
Hetas have a list of stoves on their website
http://www.hetas.co.uk/appliance/?product_type=drywet-
Andy