Surely it's better to try and resolve minor things to be civil? Just because your neighbours suck even more doesn't negate the issue at hand here, one that can be easily fixed. I think it's a perfectly reasonable request. Plenty of people like to sit in the garden even in the autumn and spring to get fresh air, especially when the temperature is just on the edge and heating doesn't have to be on permanently, so the boiler will be turning off and on continually maintain a certain temperature indoors. Seems like an easy fix with a 90g adapter to the cost of the homeowner/fitter. I wouldn't request money from the neighbour to fix a poorly thought out install. A bit of situational awareness and consderation from the installer who fits these day in and day out could have avoided the situation all together.