Honeywell L7224u error 5


Old 10-15-18, 01:18 PM
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Honeywell L7224u error 5

Just replaced my L7224U controller because the old one got fried when using a portable generator. So I simply put the wires back in the same positions in the new unit. But I get an Err 5 code, which means "Low Line; check L1-L2, 110Vac" There is 121 V across the L1 and L2 wires, same as for the rest of the house. Any ideas?
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Old 10-15-18, 03:08 PM
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If you are sure all the wiring is correct on the new aquastat,, with the info provided what I would try is removing all the wires except for the L1 & L2 and check your voltage. You should have 120, the same as just the wires.

Then hook up 1 wire at a time and take your reading after each one and see if and when the voltage drops and go from there, tracing the wire that creates the drop.

Something is causing the drop, maybe a control got damaged besides the aquastat.

Just a thought. Hope this helps a little.
Old 10-15-18, 11:46 PM
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Welcome to the forums.

Not 100% sure but that controller may be polarity sensitive.
Be sure the hot wire is on the correct Lx terminal.
Old 01-05-19, 07:57 PM
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For these kind of issues an old fashioned test light with 120 volt incandescent bulb is best.

Connect one bulb lead to earth ground/ water pipe. Other bulb lead to first black 120 vac then white. Bulb should light brightly only on the black lead. If it lights dimly there is issue someplace.

While they are good for some things, for trouble shooting, modern volt meters and neon test lights often can be misleading.

For testing 240 VAC use two 120 volt bulbs in series.
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