Baxi bermuda 551 intermittent hissing from pilot light

[Ansumstan]

Hi I have a baxi bermuda 551 back boiler. When the boiler is not fired up, i.e heating and hot water off, I am experiencing an intermittent hissing noise which seems to be coming from the pilot light area. It lasts for about 10 seconds then goes of for about 5 secs then on again etc. Is this normal and I just havn't noticed it before. If not has anyone got any idea what could be causing it. Thanks in advance for your help.
Daniel

 

[fitz1]

possible leak on your heat exchanger , or rain coming down your flue liner, or condensation.Get a corgi chap in to investigate.

 

[gas4you]

I would go with fitz's first suggestion, leaking HE