This Summer, I re-designed & re-plumbed my radiant heating system as I was having this problem: My TT Solo60 boiler could not modulate low enough in mild weather, it cycled on/off at about 5 minute rate (some called it "bouncing off the bottom") AND it would make a loud Foghorn noise for about 20 sec. on each re-fire. VERY ANNOYING! Couldn't find a fix. .................................................................................................................................................................................................................New setup: boilers only task is to heat my 80 gal. Lochnivar Solar "domestic" hot water tank (2 pipes in & 2 pipes out), no ODR, no TT control, only the tank aqustat controls firing the boiler. There is a flat plate heat exchanger between the boiler and the tank. My large domestic hot water tank acts as a buffer tank AND my domestic hot water. Boiler fires on high for about 30 min. each time to maintain maintain tank temperature !!!NO FOGHORN NOISE!!!.............................................................................................................................................................................................I know it's not condensing but it never did very much at my 8,500' altitude..........................................................................................................................................................................................When any zone calls for heat, heat is pulled out of the tank, through the heat exchanger in the opposite direction...........................................................................................................................................................................................WORKS GREAT