I have an EKO 40 and decided to continue operating it this summer due to high Propane price and I have 40 acres of forest. Due to the low demand for hot water, I only had to fill up the firebox once a day. The EKO ran flawlessly supplying 120 Degree domestic water to the house and apartment. I keep the EKO set at 180 degrees and use a heat exchanger to isolate the boiler water from the domestic and heating water and a mixing valve to reduce the water temperature to 120. This morning I went out to the Shop where the EKO is installed and noticed an over temperature code and the water temperature of the boiler was a little over 240 degrees F. Everything was running fine, the heat exchanger and mixing valve were still supplying 120 degree F. domestic heating and hot water, the pumps were running and there was no sounds from the boiler. I immediately opened the fire box and it was almost out of wood. The EKO had burned a days worth of wood in 12 hours. After a few hours the boiler temperature was down to 176 Degrees F. I turned off the Boiler, turned it back on and it began working as if nothing had happened. I found out that the bypass damper was not fully shut and this allowed enough air to enter the fire box and allowed it to burn uncontrolled. I did a little research on line to find out why the boiler continued to operate without turning the water to steam and never opened the relief valve. I found out that water boils at different temperatures depending on the water pressure. I was fortunate that I had almost 30 pounds of water pressure in my boiler. Water boils at around 240 degrees F at 26 pounds of water pressure. I guess I am lucky that I had that much water pressure in the boiler or I could have turned my hot water boiler into a steam boiler and done some damage.