I had a gas engineer come round last week to service my potterton powermax he85 last week. He said the boiler was in very good shape and there were no concerns. However yesterday I noticed a tapping sound after my shower. I opened up the front and saw that water was dripping down from a plastic pipe onto the floor. The drops stop after an hour or so (I don't know when because i went to sleep). I feel like the engineer may have loosened the cap whilst he was inspecting it. Can anyone advise if I can try tighten the item myself? Or should I wait for an engineer to come out. I've pointed to where water has started dripping in the picture: