hot water problem weil-mclain

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Old 09-24-12, 11:35 AM
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hot water problem weil-mclain

Hello....
I have a Weil-McLain P-368-WT oil-fired hot water furnace, 24 years old with a Honeywell L8124 aquastat. Aquastat set at 160/180, diff at about 15. Several days ago, shower would start off hot enough, then shortly go to cold. There's plenty of water pressure in hot water line. Furnace will only turn on when it drops to the 160 (then off at 180).Between the 160 and 180 there'll be hot water. It won't come on when there is a demand for DHW if is above the 160. Are there two temp sensors(bulbs, I guess) on the aquastat, one for baseboard heat demand and one for DHW demand? I have heard these aquastats sometimes fail at a soldered connection. Could this be the problem, and if so, is it worthwile repairing? I'm able to do that, but don't mind springing for a new one if that's a better choice. Looks easy enough to replace, but am concerned about monkeying around with a 24 year old unit that has rust/corrosion in that area (afraid of breaking a connection off). Also, there's no mixing valve going into the tankless coil, the furnace is clean and tuned. I can get enough hot water if I start the unit from cold, then wait for hot water to come. I've got the extra time it takes to go from cold (instead of 160) until it hits the high limit, which I've just temporarily reset to 200 (yeah, I know that's too high) to give me a little extra time and DHW. Can I test the aquastat in place? Any ideas??? Thanks
 
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Old 09-24-12, 12:15 PM
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Hey Larry... I bet I know you! Bluegrass? If it's you, call me, I'm home, I'll answer.

There's only one 'shared' sensor.

I'm a little unclear of your description though...

Furnace will only turn on when it drops to the 160 (then off at 180).Between the 160 and 180 there'll be hot water. It won't come on when there is a demand for DHW if is above the 160.
This sounds 'normal' to me... sort of... lemmee essplane...

With a LOW setting of 160, and a DIFF of 15:

The boiler should fire when it hits 150 ( which is the 160 setpoint, MINUS the FIXED 10 degree DIFF) and it should shut off again at 165 ( which is the LOW setpoint, MINUS the FIXED 10 degree DIFF, PLUS the 15 degree adjustable DIFF ) [ 160 - 10 + 15 = 165 ]

The LOW setting of 160 is quite high actually. In fact, you must not set the HIGH and LOW any closer than 20 degrees apart as this can cause erratic operation by the two setpoints interfering with each other.

As an experiment to see if this is the case, drop the LOW setting about 10 degrees and observe the action.
 
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Old 09-24-12, 12:33 PM
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NJTrooper...........Thanks for the quick reply...I have to run some errands, will try your suggestion, when I return, however, the furnace and DHW had been normal until last week, with no changes to aquastat settings for years....To clarify, there's hot water between the 160 and 180 WHEN THE FURNACE IS ACTUALLY RUNNING, and furnace won't come on with a DHW demand..Nope, no Bluegrass, but have a passing interest in Blue Note vinyl... jazz..(used to press vinyl records in a factory)., am writing an article for IAJRC International Assn. of Jazz Record Collectors about Blue Note.
Larry
 
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Old 09-24-12, 12:59 PM
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NJTrooper......Tried your suggestion before leaving the house...settings @150/180/diff15, ran it through a cycle, after it reached temp and shut off I ran hot water, and unit kicked on again with DHW demand....seems OK, but only thru that one cycle, however, settings had not been changed before the problem started, that's what baffles me
Larry
 
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Old 09-24-12, 01:09 PM
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Larry, how interesting that you and my friend have the same boiler ! I thought for sure you were he. I'm a swing/beebop jazz fan myself (among lots of other genre, including Bluegrass... yes, even Metal!)

(used to press vinyl records in a factory)
That sounds like a cool job! Better than pressing license plates in a prison! (not that I ever did! )

You may in fact have a cracked and intermittent solder connection on the aquastat PC board.

Monitor the system for a while and see how it goes, get back with us if it still is acting up.
 
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Old 09-24-12, 10:45 PM
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NJTrooper...........
I was out most of day and evening, hadn't has time to test out furnace fully. If aquastat has broken solder connection, can I remove it for repair without removing the sensing bulb, or does the entire deal come out? My concern is monkeying around with the immersion well assembly on a 24+ year old unit that's rusty in that area; don't want to strip or break something permanently. Assuming I get this fixed, what are good settings for the aquastat? Is it somewhat of a personal preference, or what? If lifestyle is taken into account, we have a 2,000 sq.ft. house, two zone heat, we keep it very cool in winter, mid sixties temp., lower at nite. Two person household, hot water for daily showers and occasional dishwasher use, sometimes warm cycle on laundry, but usually cold. Your thoughts on settings....Also your thoughts on what brand of furnace to replace it with, probably in next couple years...I DO like the Weil McLain...

Larrynj
 
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Old 09-25-12, 12:22 PM
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NJ Trooper...
If I understand you correctly, when the thermostats are off, and no demand for baseboard heat, the boiler is going to react to a demand for DHW using ONLY the LO setting and the DIFF, as you explained. The HI controller only reacts to a demand for baseboard heat (?). I now have settings @ 150/180/15. Plenty of hot water, however, with a DHW demand the furnace goes up to 185, shuts off, and fires again at 175, assuming the temp gauge is correct, (with hot water running continuously). Should it not be shutting off at 165, and not continuing up to the HI? Also, should I be using different LO/HI/DIFF settings in summer than I use in winter?
Thanxxxxxxxxxxxx
Larrynj
 
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Old 09-25-12, 05:01 PM
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Hi Larry,

Yes, I believe your understanding is correct.

The LO and the DIFF are for the domestic HW, and the HI is the 'high limit' which should only occur with a heat call.

Your description of operation sounds completely wrong.

I'll tell you this: Sooner or later, someone is going to be accidentally scalded. That is, if you do not have an automatic tempering valve on the outlet of the HW coil from the boiler. The potential for getting 180F hot water at the tap is very real, and that will peel skin in a NY minute! A tempering valve will limit the HW delivery to the home taps to a safe 120F. In other words, the COLD/HOT mixing is done at the boiler instead of at the tap or shower.

It does sound as though you may have a problem with that aquastat.

Should it not be shutting off at 165, and not continuing up to the HI?
That is basically correct. A little off though... let's talk about the way the LO and DIFF work together again.

There are two 'formulas' for figuring the 'cut in' and 'cut out' of the boiler for the LO setting.

The 'cut in', the point at which the burner will fire is ALWAYS (regardless of the DIFF setting):

LO SETPOINT minus 10 (this 10 SUBTRACTIVE DIFF is FIXED and separate from the adjustable diff)

The 'cut out', the point at which the burner stops firing (in the absence of a heat call) is:

(LO SETPOINT minus 10) plus DIFF (the ADJUSTABLE DIFF is ADDITIVE)

So, for 150 LO and 15 DIFF, the burner will fire:

ON at 140, and OFF at 155

Another example:

LO set to say 140 and DIFF set to say 20

Burner ON at 130, and OFF at 150

If yours in not acting this way, then:

a) someone has monkeyed with it in some way and f'd it up

b) the wiring is wrong somehow

c) the aquastat is defective
 
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Old 09-25-12, 05:13 PM
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If aquastat has broken solder connection, can I remove it for repair without removing the sensing bulb
Yes, you probably could. The sensing bulb is in an 'immersion well'. It is DRY inside that well. It's a copper/brass tube that is threaded into the cast iron. The bulb should simply slide out of the well.

The circuit board will come out of the chassis by bending out those metal 'tabs' in four places.

If you do this, my advice is to take pics of the wiring so you get it back where it belongs!

Remove the wiring, bend out the tabs, and you should be able to slide the board and the bulb out. BE CAREFUL! If you kink the capillary tube on the bulb you will definitely need a new one (you may anyway need one anyway)

Why not take a CLEAR, WELL LIGHTED, IN FOCUS, high res pic (for old folks to see) pic of the wiring in the a'stat and post it. Maybe someone has moved some of the wires into the wrong holes...

If you DO have to replace it, my suggestion is use an L7224U replacement.

Patriot Supply - L7224U1002
 
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