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Posted by HeatPro on March 27, 2005 at 16:44:36:
In Reply to: Re: Temp. overshoot posted by rick on March 27, 2005 at 16:06:39:
At the end of a call for heat, most simple control systems turn the circulator off with the burner; thus the heat that is on the fireside has time to transfer into the still water inside the burner after the shutoff. Check again to see if your control system shuts the circulator off with the burner; if so, then your observation doesn't occur.
If your burner goes off BEFORE the heat is satisfied, that shows that there is more input into the water than there is radiation to get rid of the heat, so the water is hitting the high limit, thus shutting off the burner; but not the circulator. If that happens in the coldest weather, your burner is larger than necessary, otherwise said that your boiler is OVERSIZED. As you can't make the water flow through the radiant section faster without causing other circulator problems, you might have to provide a loop-subloop piping so the true water temperature within the boiler distributes the heat evenly inside the boiler tripping the high limit earlier so the overshoot doesn't occur.