I am baby sitting my landlords Heatmoor OWB while he is on vacation.  I have noticed that when the blower comes on and the temperature starts to rise that there is a gurgling sound coming from the front and top (just above the door), right above where the hose comes in/out for water circulation in the door.  Thinking that the boiler was low on water, I put about 5 gallons of water in until it was full.  The boiling sound is still there.  Could I have a blockage in the laine or internal workings of the water chamber??  I just do not want a meltdown or warpped door before he comes back.  Any help would be appreciated.