Interesting Honeywell Aquastat Failure

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Old 04-16-10, 11:11 AM
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Interesting Honeywell Aquastat Failure

Furnace: SlantFin XL2000 Tankless
Burner: Beckett AFG
Aquastat: Honeywell L8148A (horizontal mount)
http://customer.honeywell.com/techli...0s/60-2278.pdf

Came home to a dead furnace earlier this week. Appeared no power was getting to to the furnace when a heat call was received from the multi-zone circulator controller.

Troubleshooting was interesting. The furnace relay on the aquastat did switch on when heat was called, but nothing happened. First thing I noticed is no spark when the contacts closed.

Probing around with a multimeter on the Aquastat board, I found some low, but not zero, voltages (about 4 volts AC). Knowing I should only see 120V or 24V on that board, made me think something was toasted.

I pulled the board out (untwisted the metal thingys at the corners), and found what I suspected...there was a burned trace on the back of the board. Where the relay connects to the board, the pin-through-hole solder joint on the right side had arc'ed and was open (with some residual contact giving me low but non-zero voltage). Also damaged a trace on the board just below this pin.

I resoldered the pin, and soldered a jumper wire over the damaged trace, and now everything seems fine.

I noticed a couple of these units for sale as "reconditioned"...which made me think it might be a common problem...

My questions:

1) Anyone seen this fail mode before on this type of Honeywell aquastat?

2) Is there some external cause for this? I'm thinking perhaps the burner motor is running over-current and caused the solder joint to fail. Or some other weird condition? I've serviced the burner myself with instruments for years, and it appears to run fine.

I'm trying to decide if this was just a manufacturing flaw (cold solder joint, bad solder reflow, etc.) that took 12 years to show up, or if there is some other component in the system that is bad and will cause this to fail again.

Would appreciate any insight from those that have serviced these units...appears to be a common vanilla aquastat...
 
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Old 04-16-10, 05:03 PM
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You ask all these questions for one-time failure? Imagine the questions the person has, who has put in say 4 alternators in 6 months. If it does it again, you will know right where to look.....and ask the same questions, which then would make one wonder, for sure.
 
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Old 04-16-10, 07:28 PM
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Aquastat failure

The failure you experienced is not uncommon. I actually prefer some of the remanufactured aquastats to new because of better soldering. The new ones are wave soldered & the remans I use are dip soldered.
 
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Old 04-17-10, 05:27 AM
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aquastat solder problems

Had the exact same thing happen to me. Found the same problem, fixed it the same way. Still working fine.
Steve
 
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Old 04-18-10, 02:10 PM
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Thanks!

Looks like I'm not alone on this one. Must be a gift that keeps on giving for emergency calls...

I'll probably just use my repaired one if that's a known defect, and I think its fixed pretty well. In case I need one, can anyone suggest a source for the reman?
 
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Old 04-18-10, 07:28 PM
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Reman Aquastats

I like the ones remanufactured by Sid Harvey. Only problems are (1) they don't sell retail & (2) you have to have an old one to turn in or they charge double.
 
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Old 04-19-10, 11:58 AM
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anytime there is a load going thru a board mounted relay like your burner which the aquastat controls you have a amp load on start and running thu it...even in commercial HVAC seen board relays short and anything within the area on tht baord takes a hit resistor,solder joint.the manufacturer willn't admit it but enough complaints and they might beef up the relay.if you can read the 24Vs signal for that relay to close the burner... you can wire in an external relay and close the control power to the burner to get it away from the board taking the hit.check the amperage rating on that burner and see if the board is rated or the actual relay is stamped for max amps....
 
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