Honeywell L8148 Aquastat sanity check


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Old 10-21-19, 11:30 AM
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Honeywell L8148 Aquastat sanity check

Got a new L8148 aquastat today for one that fried last week. Got it all wired up, flipped the switch, nothing. After confirming that I had a call for heat from at least 1 thermostat I jumpered the two T terminals on the board, still nothing. Question: that should force the boiler to fire correct? (cold boiler so high limit not an issue). Looking for a sanity check as I already RMAed the part as defective.

When I manually open the relay the burner and circulator fire right up no issues.

FWIW, 2 zones are hooked up with Taco zone control valves powered via a doorbell transformer hooked to the primary in. Nothing has changed in this part of the circuit but just thought I would mention it because it's super janky.
Anything else I should be checking before I rip out the new aquastat?
 
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Old 10-21-19, 12:11 PM
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If L1 and L2 had power on them..... at least the relay would close when the TT connections were shorted. Possibly a jumper was missing ? What model 8148 ?
 
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Old 10-21-19, 12:35 PM
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Correct, 120V coming In and and manually manipulating the relay fires the burner and runs the circulator. The relay does not close/open when jumpering the two T terminals.
 

Last edited by sniperpiper; 10-21-19 at 12:35 PM. Reason: Added a word
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Old 10-21-19, 12:38 PM
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It's model L8148A1017. It's an exact replacement for what was there before it fried.
 
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Old 10-22-19, 06:26 AM
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Aquastats provide contact closure to start burner. Obviously sandpiper issue is not the aquastat.

If sandpiper had a modern burner controller $64 with LCD display that shows status and history it would be a big help to understant what is going on here. https://s3.amazonaws.com/s3.supplyho...s/R7284Bro.pdf

Rather than paying $159 for old technology Honeywell L8184 sandpiper can save up to 20% annually on fuel costs with Tekmar aquastat/outdoor reset for $157 and save $2.00

https://www.supplyhouse.com/Tekmar-2...iler-4150000-p

The Tekmar 256 has LCD display and digital menus that enable system to be optimized. It requires one extra wire to keep power on at all times.

https://www.supplyhouse.com/Honeywel...tial-5477000-p
 
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Old 10-22-19, 09:36 AM
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Went back to the unit today and did some more debugging while I wait for UPS to get here.

Measured voltage across both T terminals and B2 and got 0V on both. I'm thinking it's a bad 24V transformer. I took the board out and check the solder on both T posts and have good continuity between posts and traces on the board so my only guess is the transformer is bad. We'll see when the new unit shows up....
 
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Old 10-22-19, 12:51 PM
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A brand new aquastat with a defective transformer ?
 
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Old 10-22-19, 02:36 PM
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If you've checked the continuity on both the primary and secondary xfmr windings, then the xfmr is good.
 
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Old 10-22-19, 06:44 PM
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I don't know how else to explain there not being 24V on either of the two T terminals or the fact that jumpering the two Ts doesn't suck the relay down when there is 120V on L1....
 
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Old 10-22-19, 07:20 PM
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Measure the transformer voltages directly on the leads from it. If there is no bare spot to contact use pin thru insulation.

A bare transformer not connected to anything usually does not have continuity between primary and secondary. Reason xformers are used for isolation.

When power is on, T T terminals, when not connected together should read 18 - 24 VAC. Usually one side of xformer goes to one T. The other xformer to a 24 volt relay coil. The other side of relay coil goes to second T.

Next measure coil resistance, typically a few hundred or thousands of ohms.
 

Last edited by doughess; 10-22-19 at 07:38 PM.
 

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