Re: Low heat in water boiler

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Posted by Harold Kestenholz - Hydronic Network on December 24, 2000 at 07:05:52:

In Reply to: Low heat in water boiler posted by Mike on December 24, 2000 at 02:37:35:

There are systems called one-pipe hot water systems. There is a large pipe running around the basement with smaller pipes coming off the larger pipe going to the radiation in each room. The radiation acts like an air trap and can prevent water from flowing through unless they have air vents. If your system is of this type, air will need to be bled from the fin tubes upstairs as the diverter fittings do not have a lot of force to push air pockets out once the radiation has been drained.

Unless the water is going through another loop not near the radiation, this is the only way you can have a hot supply and return and only warm tubes in the radiation.

If the explanation was not correct, and the pipes in the fin tubes are hot also, then there simply is not enough radiation or the system was designed to run at a maximum of 210F and the high limit control is set too low. There were many systems designed at 210F to save on radiation.

IF this is what happened then you have two choices:
1. have the high limit adjusted upward to permit 210 water through the system. (The old boiler and radiation was originally built for steam or water and steam funs at 215F. copper is not damaged by 210 water, just 1500F fire.)
2. Add more radiation to the rooms so there is more radiation to add heat to the home at a lower temperature of 180F.

You can learn more about hot water heat in the free lesons at

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