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.