L8124A Aquastat Settings

Old 12-29-11, 08:47 PM
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L8124A Aquastat Settings

Hi all,
I have a Utica Starfire 3 boiler with the Honeywell L8124A Aquastat
I do not use the on demand hot water anymore (Installed a separate water heater) the settings on the aquastat are hi-210 lo-120 diff-10 I have watched the boiler cycle on/off several times
when the temp drops to 130 the boiler cycles on and when the temp reaches 180 it cycles off. Is this correct? I can understand that the low temp 120 + 10 diff should turn the boiler on at 130 but why would it turn of at 180 when it is set for 210? Also I have read elsewhere that for this type of boiler it is best to have it run less often but for longer periods and since I am no longer using the DHW coil I don't need it to maintain the hot water temp but don't want to let it go cold as it seems that these type of boilers will develop leaks if allowed to cycle like that. Any suggestions on settings ? are current settings ok? Thanks, Jim
Old 12-30-11, 06:19 AM
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Your aquastat seems to be consistently "off" by a good 20F.
The L8124A is a Honeywell triple-aquastat-relay control. The high limit comes from factory with a 10F "fixed" differential (non-adjustable).
The low limit is a different story. If the differential setpoint is 10F or less (and you indicate it is set for 10F), then it is subtractive, not additive; in other words: 120-10 = 110F is the expected cut-in for the burner (not 120+10=130 as you suggest) and 120F is the cut-out (again, for the burner). The differential in this control could be set anywhere from 10-to 25F...anytime you pick a setting greater than 10F, 10F is always subtractive and the balance additive.

Since you're no longer using this boiler for DHW (Domestic Hot Water) generation, the low-limit setpoint becomes irrelevant from that end. The low-limit setting is there for two reasons, (a) to keep the water in the boiler warm enough so is able to heat-up the immersed DHW coil, and (b) to prevent the circulator from running if the water in the boiler is not warm enough (110F in your case)

Whether a boiler will run for longer periods (as you wish...and you're so right there), will depend on how oversized it is. You're no longer using it for DHW generation, which will make the boiler run less (now it is only taking care of the heat, so it has extra capacity..."it is oversized" for just the heating load). And if the boiler was oversized to begin with (something that happens more often than would be desirable), now it is even more so.

You should raise the low limit set point as it will shorten the time the boiler remains OFF after reaching the high-limit setting. It will make it cycle more often. In the absence of DHW demand, a limit setting 25-30F lower than the high limit setting is better than what you have now.

You do not mention if you boiler is condensing or non-condensing (for the setting shown it'd better be non-condensing), gas or oil. Or the M/N. All that info would be helpful. Utica has a superb website, check them out.

Last edited by pflor; 12-30-11 at 06:36 AM.

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