New L8148E different from old?


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Old 12-29-12, 10:00 PM
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New L8148E different from old?

My old Honeywell L8148E aquastat doesn't have adjustable differential. Not sure if that means there's NO differential or if it's preset because this info isn't in the manual. I spent a few nights at my hot-water-baseboard-heated cottage and the first night I couldn't get to sleep right away. I was laying there listening to the boiler short-cycle and wondering why the burners come on even when the boiler is still hot from the previous cycle. So that's what raised the question in my mind--does my a-stat have a differential at all? I'm sure I could be saving fuel if the circulator came on without the burners--until the water temp drops to the lower setting.

Related question: Is a new replacement L8148E built to be compliant with the new 2012 rules...or is there a non-digital replacement that would do what I want?
 
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Old 12-30-12, 07:43 AM
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The only L8148E aquastats that I am familiar with is the L8148E 1265 and L8148E 1299. Both have a fixed 15 degree F. differential. Neither are what I would consider "digital". You can find both listed at PEX.com complete with specifications.

Two years ago I replaced my 32-year old L8148E with a L8148E 1299. The old one did not have a 1265 or 1299 on it but the specs match the 1299 best.

If you didn't have a "short" cycle you would be running your circulator pump a lot longer and you still need to get the same BTU's in the house to keep it warm so I would not expect any cost savings. Better to add insulation to the house.

I am not familiar with the 2012 rules.
 
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Old 12-30-12, 09:04 AM
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Agreed on the insulation, always. It makes the most economic sense if it's possible to accomplish. It's fuel you pay for once.

Guy, if your system is 'bouncing' off the high limit constantly (sounds like it is), then you might have a system that is a good candidate for the "Heat Manager" system.
 
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Old 12-30-12, 11:46 AM
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It was bouncing off the HL because it was 42F inside when I got there (21F outside). T-stat was set to maintain 50 but it had failed (new unit). No idea if it ever got below that 42F but there was no damage. After the house had warmed to the core by the 2nd night things were normal--but I still don't like that there's little or no differential. I was hoping to replace the a-stat with a new one, IF the replacements are built to the new standard or feature an adjustable differential to keep the burners from lighting when the water is still at 180F. After all the info I've read here about lowering the HL & increasing the differential I was surprised to find I had NO diff. adjustment, and the lowest setting on the HL is 180.

I plan to gut the interior when weather improves and more insulation is planned, of course. I need to first make it through the winter at this new (to me) cottage.

BTW After I get my replacement t-stat I plan to wire a 2nd one in parallel in the basement so I'll have a redundant control if the primary one on the wall should fail again.
 
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Old 12-30-12, 04:40 PM
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One of the attributes that the different 'flavors' of aquastat affect is the temperature range. In the olden days, many of them were like 180-240 adjust range.

An 8-10 degree diff was not uncommon at all.

Take a look at the Beckett AquaSmart 7600B

Patriot Supply - 7600B0001U
 
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Old 12-30-12, 05:42 PM
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Anything simpler, non-digital? KISS has always worked best for me.
b
 
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Old 12-30-12, 07:11 PM
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If you have a spare tapping on the boiler into which you can insert an immersion well, you could install some flavor of 4006 a'stat and wire it in series with the high limit switch on the existing a'stat.

You could also do same with a 'strap-on' version on the supply pipe out of the boiler.

I believe the diff is adjustable to 30 on some models. You would set the setpoint of the add-on a'stat a bit lower than your high limit, and run a 30 diff.

The 4006 would 'take over' from the existing a'stat with the added benefit of having a redundant HL control.

I did this on my old boiler at one point and it worked well.
 
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Old 12-30-12, 07:22 PM
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I already hve a redundant HL on the return pipe that interrupts the T-stat if exceeded. I could rewire that to break the gas valve signal until the temp falls below the setpoint. If connected to make on fall I lose the redundant HL protection but at least I can experiment with the idea for a few days. Sound do-able?
 
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Old 12-30-12, 07:32 PM
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As long as it has the adjustable diff you are looking for and it's not the manual reset variety, I suppose you could fool with it.

What model is it?

How is it wired now? In the AC supply to the system?
 
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Old 12-30-12, 08:55 PM
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I thought the "differential" comes from setting the 2nd dial below the setting of the 1st (a-stat)...so this 2nd control wouldn't need its own differential adjustment(?)

I don't know the model but it's a SPDT strap-on like this one:
White Rodgers 1127-2 Control (Strap-On)

 
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Old 12-30-12, 09:15 PM
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Ohhhh, I see what you are thinking... I don't think that will work though.

You want the boiler to heat to 180, then stay off to say 30 below that, right?

The way they have these things set up is sometimes confusing... the SETPOINT DIAL, the one that is visible in the window, the fixed pointer at top center, is actually the LOWER of the two settings. The left hand pointer, the adjustable one, is the HIGHER of the two settings.

See following post for more info...

The last time I did this I wired the second a'stat in series with the HL in the existing a'stat.

Since the diff is negative I maxed that out and just set the setpoint on the added a'stat a tad below the one in the existing a'stat.

With this setup the added a'stat assumes control. Boiler heats and hits the limit (indicated by the adjustable left hand pointer) in the added a'stat , burner shuts off, cools to diff (indicated by the fixed pointer) in added a'stat, comes back on.

HL in existing A basically does nothing because it's set ABOVE the limit in the added one. It will act as a secondary aux high limit.
 

Last edited by NJT; 12-30-12 at 09:35 PM.
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Old 12-30-12, 09:27 PM
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In your 8148, remove one of the wires on top of the HL snapswitch.

Run wires from the RED and BLUE on the WR into the aquastat.

Wire nut one of the wires to the wire you removed from the HL switch

Connect the other wire to the terminal on the HL switch that you removed the wire from.

Set the left hand pointer to max diff, all the way to the left. (I believe this will give a 30 diff)

Turn the main dial so that 180 lines up with the left hand pointer.

This should put 150 under the main dial pointer.

Set your existing high limit to say 200 as a secondary backup.

Your burner will cut out at 180 and cut in at 150.

...As long as the model you have has the adjustable diff, some of the 1127 models do not.
 
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Old 12-31-12, 10:28 AM
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Your wiring is what I had in mind but I think my strap-on a-stat has only a single dial, fixed diff. I thought if I set the 8148 to 180 and the WR to 160, because of the fixed diff in the WR it would close at about 150 and the 8148 would open at 180--giving me the burner range I want. Is my thinking correct?

If the above is correct then how can I keep the circulator running when the boiler hits the upper limit? Why are boiler control aquastats designed so when you hit the high limit everything stops--trapping the heat in the boiler?
 
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Old 12-31-12, 02:31 PM
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Is your 1172 a SPDT ? three terminals? RED WHITE and BLUE?

Is my thinking correct?
Even though the W-R is fixed diff, it still has a diff, and it's probably 10F.

So, say you set the W-R to 160... it will MAKE the R & B contacts at 150 and BREAK them again at 160. So no, it won't work. You need a model with an adjustable diff and wire it so that it can assume total control of the burner with the 8148 providing redundant backup HL.

Why are boiler control aquastats designed so when you hit the high limit everything stops
They aren't! Is yours doing that?

In the presence of a CONTINUED HEAT CALL, the burner will cut off at HL, but the CIRC will CONTINUE to run.

On the other hand, when the heat call ends, the burner AND circ will shut down.
 
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Old 12-31-12, 10:10 PM
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I see your point on the 1127. 2 high limits can never work together as a differential because the higher one will never get hot enough to switch.

No problem with the operation of my L8148--it's my mind that malfunctioned. I was thinking the relay opens on HL but of course that's wrong. The relay stays closed as long as the thermostat calls for heat. The burners are on or off in response to the limit(s), AND the relay is closed.

Thanks for the help. It looks like it can't be done as an immersion unit without going to a way more elaborate digital--and perhaps riskier--aquastat.
 
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Old 01-01-13, 09:00 AM
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looks like it can't be done as an immersion unit
It could if you had a spare tapping on the boiler, do you know that you don't?

Why not replace the existing 1127 with a strap-on model that does have an adjustable diff?

Wouldn't it still qualify as an 'auxiliary high limit' in any case? I mean, you would still have the redundant high limits in place, right?
 
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Old 01-01-13, 11:29 AM
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I guess I just dont trust control of the boiler to a strap-on a.stat. I do have 2 open taps on the back of the boiler.

This thread was prompted by a statement in the aquastat "wish list" thread that all new aquastats are compliant with 2012 DOE rules and feature pre-purge. That definitely isnt true for all existing model numbers, but MAY be true for programmable digital controllers.
 
 

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