I've got a brilliant one. It actually happened to family friends back in the 1990s, however they were the most down-to-earth bunch we know and not likely to invent things.
They had recently moved into a new (to them) house. It had a really huge living room which was because the previous owner - a young, semi-professional snooker player, had the snooker table in there. Sadly he had suffered from chronic depression and killed himself (hanged himself in that room i think). They weren't superstitious though and this didn't bother them (not sure they told their two DC that fact though.) They had a DS - about 10 I think, and a DD - about 8.
Shortly after they moved in they would regularly wake up in the morning to find all the windows on the ground floor open. They assumed this was their DS and told him to stop due to security etc. He point-blank denied any knowledge and was quite annoyed about the accusations.
This happened again and again, and the mother of the house was also suffering from terrible headaches. They never thought that there was anything supernatural about this but maybe thought one of the DC was sleep-walking.
Anyway - a few weeks later they had problems with their heating and a heating engineer was called. The engineer became very alarmed and told them that the boiler had to be condemned and that they were incredibly lucky that something terrible had not happened. It transpired that the boiler was pumping out Carbon Monoxide poisoning (which was the likely cause of DMs headaches).
The boiler was immediately replaced and they never experienced the windows being opened in the middle of the night again.
They are CONVINCED that the ghost of the snooker player was responsible for opening the windows in an effort to prevent them from getting too ill from the Carbon Monoxide and they also believe that, with hindsight, the fumes were responsible for his sudden and fatal depression.
Quite a nice ghost story but also so very sad.