Damp patch on inside wall

[bww12pwcf]

I have a damp patch that keeps appearing on the inside wall above fireplace. This does not always seem to appear when it rains, even if heavy, we have had quite a lot of rain in the last few days. But I notice that the trouble appears when it is humid, and not raining. There is a gas pipe, feeding the gas fire, which is of an open type effect coal. I am thinking that the cause, maybe, condensation caused by the gas pipe. This patch does dry out, not leaving too much of a stain. There is no mould. I look forward for any comments. Thanks.