L8148E Lifetime ? reposted from furnace thread

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Old 12-11-11, 07:27 AM
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L8148E Lifetime ? reposted from furnace thread

How long can I expect my 2 year old Aquastat I8148E to last ?

My first one was installed in 1984. It was changed out two years ago, I can't remember why. The new one went off of warranty a year ago. A technician from the same company came out last week and claimed it was bad and needed to be changed out again. I paid him for his time and told him I would handle it. The boiler wouldn't fire. Now it does.

I just wonder how long before it truly fails? Further which component should quit first ?

It is used in a hydronic heating system with three circuits. I usually turn the system on in November and off in May. Lake Tahoe area. Can't recall the name of the boiler. Its 27 years old.
I am not on site.
 
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Old 12-11-11, 10:45 AM
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They've been known to last for decades... usually a reliable part... but of course, in recent years due to economics, and 'offshore' labor, the quality of nearly everything seems to suffer these days.

I can't speak for the skill or honesty of your technician, I don't know him, but of course that's always something to be questioned... just keep that in mind.

Tell us a bit of the 'back story'... you said the boiler wouldn't fire, but now it does.

When did it stop working? Did you do anything but call the tech? and did it start working immediately after he left?
 
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Old 12-11-11, 11:48 AM
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Thank you NJ Trouper. I hear you on the decades. My first unit after 25 years, looks like it might still have usable components on it. The board and the wiring on the board are still all good. I suspect the transformer is still good. I haven't inspected the relay yet but some burnishing of its points ought to improve it some. I can't evaluate the temp probe yet but may play with it later.

As I have thought about this some, I suspect the relay is the part that would fail first before the transformer. Don't know about the probe.

There is a back story which I would rather not belabor. Bottom line I fired the technician after paying him for his time at the point that he told me he needed to change out the fairly new (2 year old) L8148E. That "new" L8148E installed two years ago, contains a fuse in line with the power to the boiler. It had failed for unknown reasons some time after I turned the system off last May and when I turned it on again in November.

After a bit of scratching my head and scurrying around the internet looking for diagrams, I realised this and that I could modify the jumper plug to bypass the fuse. It was not difficult to accomplish this repair, I am surprised the tech didn't do this during the hour that I paid for or at least replace the failed fuse. It was the kind of support that I expected of him when I placed the service call.

That fuse is there to fail on the first use of a damper control circuit. My system has no damper and no damper control. So it shouldn't have failed. Since it did fail, no power was supplied to the boiler. That symptom led me quickly to finding this fuse and learning about it. I would expect this level of knowledge to be widely known in the service industry.
 
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Old 12-11-11, 12:58 PM
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I haven't inspected the relay yet but some burnishing of its points
I think the single biggest failure point on those aquastats is cracked, cold solder joints where the relay is soldered to the PC board.

Be careful burnishing the contacts. NO SANDPAPER! You'll remove the plating and then they'll really wear. I usually recommend a piece of shirt cardboard saturated with a good contact cleaner like DeOxIt Gold... but honestly, unless there's a dead spider stuck in there, I don't think that's gonna be your problem.

I would expect this level of knowledge to be widely known in the service industry.
So would I... but frankly, you need to lower your expectations... Sadly, in today's age, the word "Technician" has come to mean anyone who knows which end of the screwdriver goes in the screw.

I wonder why that fuse failed... do you have a multimeter that can measure current?
 
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Old 12-11-11, 01:26 PM
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Yes, my meter can read current flow. My suspicion is that the fuse is not tolerent of much current. As it sole purpose per the Honeywell spec sheet is to fail on first use of a damper control circuit. The combined current draw of the boiler circuit and the damper control circuit is enough to blow this fuse. So its tolerance must be pretty low in the first place.

This is a new feature. It was not present on the original L8148E board 25 years ago. It was the first thing that caught my eye after cleaning up the sloppy wiring. inside my aquastat.
 
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Old 12-11-11, 03:46 PM
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I believe that fuse actually blows due to the presence of a direct short circuit when the damper is plugged in. Could be wrong about that, but that's my recollection... [NJT edit: I just looked at the docs, and that's exactly what happens when the damper is plugged in... DIRECT SHORT blows the fuse, on purpose.] I'm not sure of the amperage of it ... I don't think it's stated in any of Honey's docs because it's not important... and they don't want it being replaced anyhow.

The purpose of that fuse is to prevent someone from unplugging the damper and firing up the burner and killing themselves, not for overcurrent protection. It's a 'fail safe' device.

I would think that in your case it was a simple failure of the fuse itself, and likely not caused by overcurrent, but if you are adventurous and can determine where to measure the current draw of the gas valve, go for it... remember that it's AC current you will measure.

Doing this would at least tell you that your valve isn't drawing too much current and possibly nearing 'end of life' for that reason.
 

Last edited by NJT; 12-11-11 at 04:55 PM.
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Old 12-11-11, 04:25 PM
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Its a bit hard for me to conceive of "a simple failure of the fuse itself" not associated with overcurrent resulting in a blown fuse. Maybe a large temperature swing ? While on the other hand, I could see the older boiler current demand pulling more current than expected in the form of a transient at startup thus blowing the fuse. In any case I will check it out as best I can some time next week. For the past two winter seasons the current flow was through this fuse, that may have weakened it. It seems like this board was designed to support a damper control. My system not having one is definitely behind the times and not exactly compatible. Rejumpering the bypass plug was probably the best of the two ways to fix this situation.

Do you have any opinion on how long the temp probe should last ? Also what might be inside that hunk of metal ?
 
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Old 12-11-11, 04:54 PM
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Its a bit hard for me to conceive of "a simple failure of the fuse itself" not associated with overcurrent resulting in a blown fuse.
I know what ya mean... but it happens. I see it all the time in my 'other life'. I have actually observed the fuse element inside those little 3AG glass fuses 'flex' when load is first applied... and not an OVER load either... normal operation. A fuse is a component, and they have a given MTBF (Mean Time Between Failure) just like a transistor, a diode, a car, an M1A1 tank, etc.

Do you have any opinion on how long the temp probe should last ? Also what might be inside that hunk of metal ?
As long as the probe and capillary tube is not damaged... probably forever... but not so the 'bellows' that is attached at the end of the capillary. If that part of the system were to fail, I would expect it to be by leakage of the bellows. Certainly, decades, maybe not quite as long as the older better built ones, but a long time.

I believe that there is some sort of 'wax' inside. Expands when heated, pushes on a lever, trips the micro-switch in the high limit assembly.
 
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Old 12-11-11, 05:17 PM
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I had a new built-in Whirlpool microwave. It ran fine for two years, and then the internal fuse blew for no apparent reason. I replaced the fuse, and since then it's been fine. If you flick one of those glass, tubular fuses with your finger, you can see the element vibrate - so they are a bit fragile. Regular 15A+ Edison screw-in fuses and larger cartridge fuses don't seem so fragile.
 
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Old 12-11-11, 05:36 PM
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Thanks for the education, you guys are great!

The fuse in question is a little tiny thing smaller than an old style resistor with two wire leads. Its body diameter is not much thicker than its wire leads, it is mounted on the mother board of the L8148E.

The burnishing tool I have, I inherited in the 1960s, it looks like a pen and has exchangable tiny blades for polishing points. My father probably bought it back in the 1940s when burnishing points was more in fashion.
 
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Old 12-11-11, 05:39 PM
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I believe that there is some sort of 'wax' inside. Expands when heated, pushes on a lever, trips the micro-switch in the high limit assembly.
Volatile fluid. When the temperature increases so does the vapor pressure, thereby actuating the switch(s).
 
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Old 12-12-11, 07:46 PM
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Is that the same as the bourbon tube? Going to have a shot of that now as a matter of fact, bourbon that is.
 
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