Re: Relief valve - system over-pressure?

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Posted by Harold Kestenholz - Hydronic Network on March 15, 2001 at 13:11:40:

In Reply to: Relief valve - system over-pressure? posted by Gustin Kiffney on March 15, 2001 at 10:44:42:

Your system has worked for decades without a circulator and not having one is not a cause of your problem. If a person came into a car shop and said the car was overheating, the mechanics would hopefully not tell them that they have to install a bigger water pump on the engine - same here.

The immediate problem is that the expansion tank is waterlogged. It needs to be drained. If there is nothing on the system to accomplish that, then you need to install the proper shutoff and drain valves to accomplish that. Then your water relieving problemn will disappear.

The next task is to make sure your high limit works as it is supposed to - that is, shut off the burner when the temperature is reached on the dial. This can involve a new limit control and cleaning of the well where the control sits. It is also good at this time to install another high limit control, one that straps on, on the outlet pipe of the boiler, so that you have definite and proper temperature limitation.

Another task is to reduce the oil burner input rate so the system can heat more gently over a longer period of time. The task of the radiation is to eliminate all the heat the boiler can make. The fact that the boiler can exceed 180F is proof that the input rate is higher than necessary. Reduce the input (nozzle size) until the water can not go over 200F; then the boiler water will not rise boyond the necessary temperature to heat your house.

You still can install a circulator on the outlet of your boiler (which is the best place to do so and recommended by ALL boiler manufacturers for the past 50 years) but you do not need one. If you do install a circulator, buy the smallest, weakest one you can find because it doesn't have to do any significant work. You can read more about circulators, locating them, and more in the free lessons at

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