Yesterday, I asked about options for replacing my Burnham Series 2 boiler that sprung a leak after only 9 years of service. Several of the comments suggested that a bad casting was not a likely cause and there may be problems with my system that I should identify and fix first.

According to my plumber, the boiler section has been leaking for some time and part of it is corroded. From some of the comments I received I understand that air in the system and low return water temperatures can cause the corrosion problem o that I am experiencing. As background, the series 2 heats a radiant floor section that has a mixing valve controlled by a Viessmann Dekamatick HK1, 3 conventional circuits with fin/tube in the rooms, and a loop for the hot water heater.

Now that fall is here, the heat was on this morning and I noticed that the return line was not hot and only comfortably warm to touch. The outbound line was too hot to touch. At that time, the boiler was not running and the only circulation pump running was for the radiant heat. Does this mean low return water temperatures?

As for air in the system, the water supply valve is in on position and I assume it always has been. With a continual slow leak in the boiler, turning it off doesn't seem like a good idea. However, I did have problems with the radiant heat last year. One, the battery died on the Dekamatick control so it wasn't working and there were sloshing noises at the mixing valve, and second, there was only low heat from the radiant system and gurgling noises from the tubes and many of the tubes remained cold. I called a Viessmann specialist and he reset the Dekamatick, and did something to get rid of the gurgling. He did say that the manifold thing were all the radiant tubes come out of, was mounted upside down, but that he thought what ever he did would fix things. From a temperature perspective it did and there have been no more gurgling noises. But, all this suggests somehow air got in my system.

Before I spring for a new boiler, whatever the type, what should I do or have done to make sure the next boiler doesn't meet the same fate?

Thanks in advance for all your comments.