I would reiterate the dangers of carbon monoxide poisoning, especially if you do not have a gas boiler serviced regularly.
We moved house last year and our vendor was reuired to produce a current boiler service certificate. As fas as we can work out the boiler had never had a regular service since installation 15 years ago. When the service man came and serviced he boiler, he promptly disconnected it because it was emitting highly levels of carbon monoxide and it could not be reduced to a safe level. The boiler was in a cupboard between the bathroom and the owners bedroom and the wall was just one thickness of match boarding. We were very lucky our purchase was not an executor's sale.