Triple Aquastat Honeywell L8151A

Old 10-19-09, 09:25 AM
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Triple Aquastat Honeywell L8151A

I found a description of how triple aquastats work at
Guide to Setting & Wiring Heating System Boiler Aquastat Controls, how to set the HI limit LO limit and DIFFerential dials on controls like the Honeywell R8182D Combination Control Aquastat

I think I may finally have figured what my aquastat is doing and I now believe I don't need the Low Limit at all on my aquastat. I have an oil boiler with an indirect tank for DHW and 3 baseboard zones and 2 radiant zones. All the water for heating and DHW comes off one supply pipe. This is my first house with a boiler so for 3 summers I left the settings at Hi=190 and Lo=160 and my boiler would come on for a few minutes several times a day for no reason. Now I figured out that it was maintaining the 160F temp even with no call for heat or DHW. This past summer I set the Lo=100F (as low as I could turn the dial) and Hi=160F. We had plenty of DHW and I used about 62 gallons of oil for May-September. Less than half of past summers. After reading the info at the link above I think I can simply disconnect the low limit on the aquastat as they show in their post. They remove the blue wire that is next to the Diff dial and this disables the Low limit. The only problem is that I think they are doing this on a R8182D triple aquastat. I checked my documentation for my L8151 and there is no mention of how to disable the Low Limit. I tried calling Honeywell, they were useless. Any thoughts? Ideas? Thanks.
Old 10-19-09, 04:37 PM
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One thing you should be aware of is that some boilers will begin to 'weep' when they cool off, after having spent their entire lives as a 'warm start' boiler. This is something that you have to watch for.

What make/model boiler do you have?

SHAME ON INSPECT-NY for suggesting that boiler operating controls are modified! It will VOID the UL listing, which in the event of a tragedy (house fire for example) gives a homeowners insurance company a 'foot in the door' to denying coverage... so, for that reason, we can't/shouldn't offer any 'how to' advice on that subject.

I will tell you this though, for informational purposes only... doing ONLY the blue wire trick still leaves the circulator under control of the low limit control.

Of course Honeywell won't talk to you... for the reasons above... liability and litigation. That and the fact that they are so big the chances of finding someone who knows more than how to answer the phone and process invoices is nil.

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