Some of the key things to look out for when you're buying a second hand boat are:
A 'live aboard' and a 'holiday' narrow boat are very differently equipped.
If you own or hire a boat merely for your annual fortnight's cruising holiday, the boat's electrical and heating systems can be fairly straightforward. Summer cruising puts little strain on such systems - electric lights are only needed for a few hours per day in summer; and it's warmer. You are more likely to eat out at a canalside pub rather than stay on-board and watch a 12 volt television. You may cruise for up to 8 or 10 hours per day.
Contrast that to living aboard for all or a substantial part of the year. Without the pressures of a time schedules, and with winter 'stoppages', there will be days when you don't move the boat at all.
During the short winter days you will need the lights on from 3.30pm (rather than 9.30pm in the summer). For occasional spring and autumn cruising, the cost of heating your boat may not be an issue - long term winter heating costs are a different matter. Boat heating in winter needs to be efficient (warm without excessive condensation) and cost effective.
A 'live aboard' boat's heating, electrical & charging systems must be efficient, and preferably integrated in use, for comfortable all year round cruising.