The boiler man did the annual service this afternoon. At 5:30pm the hot water switched on and the whole system was much noisier than usual. The noise didn't seem to be coming from any one place. Also, the pilot light in the boiler was off and it took several attempts to ignite it. I've noticed that the lower of the two red taps in the picture is horizontal, i.e. off, but I can't remember if this is its normal position or not. Can anyone advise?