testing/troubleshooting Honewell aquastat

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Old 11-02-08, 01:40 AM
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testing/troubleshooting Honewell aquastat

Hi, I've had a problem with my Honeywell aquastat (marked as L8124A/L8151A) in that no matter how the limits are set, the domestic water is way too hot; the temperature gauge on the front of the burner confirms that it's rather above the high limit. So I figured the temperature bulb was no good. My dad, who always seems to have spares of everything, had a couple of newer Honeywell aquastats (both marked L8124A, C), one used, the other looked unused (in fact, the bulb was taped in place on the back of the box, and the screws looked untouched). I say they're newer looking because the original has all standard screw terminals, including on B1, and the newer ones have Phillips screw terminals, with B1 being a spade connector. (So I guess I'm just assuming.)

So tonight I replaced the old aquastat with the one that appeared unused. But it didn't work, the burner didn't start either for heat or domestic hot water. I tested and made sure there was 120 volts at the line in. Crossing the T terminals had no effect, and manually (with a wooden stick) closing the contacts had no effect. Bad aquastat? So I replaced it with the other newer-looking but used one. Same thing. I put the original back in place and the burner started right up. I'm left scratching my head.

I can see my dad having one dud, but two? Is there any way to test the aquastat's functionality before I assume they're scrap? Is there something I'm missing? (Probably something that will make me smack my head, right?)

Thanks for any help or insight.

--Bob
 
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Old 11-02-08, 07:36 AM
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You could hook up a line cord to the L1 and L2 and bench test.

With the unit powered, using a multimeter set to range appropriate for 24 VAC measure between T and T (with the terminals open). You should see 24 VAC there. Jumpering those contacts should cause the relay to pull in.

If not, I suppose it's possible that they are both defective... were they garage sale 'finds' ?
 
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Old 11-02-08, 07:58 AM
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Well, with the aquastat installed on the burner and with 120v showing between L1 and L2, I did in fact test for voltage between the T terminals and found none, and crossed the T terminals with no effect.

Not garage-sale finds; my dad used to build houses and then owned a rental property and generally did most of his own repairs, so I'm guessing the one that appears unused was never installed and the one that was used may have been a "pull" but I would think he'd toss it if he knew it was no good.
 
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Old 11-02-08, 09:06 AM
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did you check for 24Vs on the TR side of the 1K coil to the other T.if you jump T to T that 1K relay should close bench test all those controls your using for that first(check for continuity on those 1K coils).the LO limit is for domestic water,and the HI limit is for the water for the heating system....burner/circ
 
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Old 11-02-08, 02:54 PM
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Another thing you can check ... sminker mentioned "1K coils" ... with the unit NOT powered, set your meter for the OHMS scale, and measure the resistance between T and T ... If the transformer OR the relay coil is open (NG), you will read "OL" ... or open circuit ...or maybe 1-2 Kohms if they are both good ...
 
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Old 11-02-08, 06:31 PM
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Well, I think I just answered my own question. I decided to take the circuit board out of each of the "new" aquastats and look at the back side. On each of them I found a trace burned right off the board right below the S2 connection of the J1 jumper. This wouldn't be a sort of fusible link, would it?

So now the question is whether to solder a bit of wire on to restore continuity, or just go buy another aquastat (most likely an L7224).

--Bob
 
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Old 11-02-08, 07:24 PM
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Why not try it ? Test it on the bench first of course ... but what's the worst that can happen ?

Trace probly got burnt by improper hookup ... and might be all that's wrong with them.

Whatcha got to lose ?
 
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Old 11-02-08, 09:35 PM
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Yup, that seemed to do it. On one of them at least. I'll have to check my soldering work on the other, and if that's okay then it's got some other problem.

--Bob
 
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Old 11-03-08, 03:34 PM
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Go to OHMS... check across the secondary (POWER OFF!) of the transformer... Don't know the exact ohms you will see, but it definitey WON'T be OPEN ... same thing on the relay coil ... probably about 1KOHM across that coil ... check the primary of the transformer for an OPEN condition also ...

I betcha someone put line voltage on the T T terminals...
 
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Old 11-03-08, 03:36 PM
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Burn it in ...

The one you fixed... hook up line cord, jumper T T , and let it sit on the bench energized ... make sure transformer and relay don't get frying hot quickly ... that might indicate shorted turns on the transformer. Cycle it a few times, 1/2 hr on, 1/2 hr off ... etc .
 
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Old 12-19-13, 12:10 PM
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NJ Trooper,

I was reading your posts all morning in an attempt to diagnose some issue that developed overnight. Long story short, I woke up to find all zones calling for heat but the burner was not firing. After fiddling with some things, I shut off power to the furnace for a few minutes and when I turned it back on, I could see and hear the relay engage on the aquastat (Honeywell L8148A - oil) and the furnace fired. Intermittently during the day, zones have been calling for heat but the furnace did not fire. Once again I shut off power to the furnace, let it sit for a few minutes and then turned it back on - it fired. I started to troubleshoot the aqua stat as described above but could use a little more help.

I cleaned the relay contacts. When I jumper the T T, the relay engages. When the burner is off, I have 24VAC across the T T terminals and no OHMs (open). This is where I get lost. Can you walk me through the next steps of where should I be looking to test? I am a little frustrated because this now seems to be happening intermittently and I don't want to spend $200 on a new one if I am wrong. Thanks.
 
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Old 12-19-13, 03:41 PM
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Hi Bay,

I am going to move your question to it's own thread after I see your replies. I'll use the same title so you can find it easily.

First, my standard warning, I know you know this, but I have to say it:

WARNING! EXPOSED 120VAC INSIDE BOILER CONTROLS! DO NOT TOUCH ANY TERMINALS! YOU CAN BE KILLED!

Please begin by answering ALL questions:

Have you at any time had to push the reset button on the oil burner control in order to get the burner to fire? Or is is simply not starting at all?

When there is a call for heat, exactly what is the sequence of events?

We know that the relay pulls in, that's good...

Is your system pump wired to C1 and C2 on the aquastat? DOES THE PUMP RUN?

Your burner is wired to B1 and B2 on the aquastat. When the relay pulls in, are you saying that NOTHING HAPPENS AT ALL at the burner? The motor does NOT RUN?

Using your multimeter set for 120V AC, CAREFULLY! place the probes on B1 and B2 terminals. When the relay pulls in on a call for heat, you should measure 120VAC on B1 and B2.

Do you?
 
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Old 12-19-13, 06:31 PM
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Thanks for answering.

I pushed the reset first thing this morning as I thought it might be an issue with the burner. That had no effect.

When there is a call for heat, the circ pumps start and the light for that zone comes on. Since I posted my earlier message, the relay is not engaging, even when all zones are calling for heat. However, if i place a jumper across the T T terminals, the relay clicks. if I do it a few times, the relay eventually will engage and the boiler will fire. Since that is happening, i assume i am good to the T T terminals, i.e. if i removed the jumper and there was a problem with the stat/control wire, the relay would disengage.

C1 and C2 are not used. The aquastat is controlled by a Taco 4 switch relay panel.

The boiler just reached temperature (170) and shut off, although the zones are still pumping. The relay is still closed and now there is no voltage across T T.
 
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Old 12-19-13, 06:57 PM
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OK... should have mentioned the Taco panel in your first post...

Need to tell me about that. Is it an SR panel that controls separate pumps for each zone?

Or is it a ZVC panel that controls a single pump and electric zone valves for each zone?
 
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Old 12-19-13, 06:59 PM
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SR panel that controls 4 individual pumps - 3 zones plus indirect h/w heat. The priority zone setting is not used.
 
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Old 12-19-13, 07:10 PM
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Since I posted my earlier message, the relay is not engaging, even when all zones are calling for heat. However, if i place a jumper across the T T terminals, the relay clicks. if I do it a few times, the relay eventually will engage and the boiler will fire. Since that is happening, i assume i am good to the T T terminals, i.e. if i removed the jumper and there was a problem with the stat/control wire, the relay would disengage.
Unless I'm not understanding what you are saying here, I suspect that your logic may be somewhat in error...

the relay is not engaging, even when all zones are calling for heat.
Do you mean the relay in the aquastat is not engaging?

However, if i place a jumper across the T T terminals, the relay clicks.
Here's where I think we start to go astray... maybe...

You are putting this jumper across the T T terminals in the aquastat when all the zones are STILL CALLING? and getting a CLICK?

This is telling me that there is a problem with the TACO panel NOT SIGNALING the AQUASTAT to fire.

If the Taco WAS signaling, you would not have any affect by putting a jumper across the T T because the Taco would already HAVE those two points connected.

if I do it a few times, the relay eventually will engage and the boiler will fire
It sounds to me like you actually have TWO PROBLEMS.

If the burner does not fire the FIRST TIME you short the T T together, then you have a problem in the aquastat ALSO.

Since that is happening, i assume i am good to the T T terminals, i.e. if i removed the jumper and there was a problem with the stat/control wire, the relay would disengage
Not necessarily...

The HOLDING CURRENT on a relay of that type is FAR LESS than the current required to pull it in from open.

IF your Taco panel endswitch relay is 'flaky' ... by that I mean not making 100% contact at ZERO OHMS, but rather only making a WEAK connection, it might not be enough of a connection to pull the relay in from open, but it MIGHT be enough to HOLD IT once you've pulled it in with the jumper across the T T terminals.
 
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Old 12-19-13, 07:15 PM
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SR panel that controls 4 individual pumps
Good... safe to presume that it's an SR-504 then? you have no spare 'channels'?

That panel has an ENDSWITCH that is wired to the T T in the aquastat, correct?

You said earlier that when NO zone were calling for heat, you had 24 VAC on the T T terminals, correct?

When all zones are calling for heat AND THE BURNER DOES NOT FIRE, what voltage do you have on the T T at that time?
 
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Old 12-19-13, 07:28 PM
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Holding current is less than closing current - interesting...didn't know that.

Yes, your logic seems correct about the Taco panel. To that end, should I start with replacing the "ice cube" relay and see where that gets me? There are 5 smaller 24VAC ones and then one that is marked as 120VAC. Is it the 120VAC relay that may be flaky?
 
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Old 12-19-13, 07:32 PM
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That panel has an ENDSWITCH that is wired to the T T in the aquastat, correct?
-Correct

You said earlier that when NO zone were calling for heat, you had 24 VAC on the T T terminals, correct?
-Yes, I believe that is what I measured earlier to day.

When all zones are calling for heat AND THE BURNER DOES NOT FIRE, what voltage do you have on the T T at that time?
- I believe I did not have any voltage across T T at that time.
 
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Old 12-19-13, 07:32 PM
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What exact model SR panel do you have?

- I believe I did not have any voltage across T T at that time.
Be sure. Test again if you have to.

What you have just said would indicate that the problem is NOT in the Taco panel.
 
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Old 12-19-13, 07:44 PM
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Yes, sorry - it is the SR504.

When all zones are calling for heat AND THE BURNER DOES NOT FIRE, what voltage do you have on the T T at that time?

- I just turned up the thermostat but, because the water is 150+, the furnace is not be told to fire; the pump is just circulating so it may be a little while before the panel call for it to fire.

Realizing the hour, I appreciate your time (and patience).
 
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Old 12-19-13, 08:02 PM
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Realizing the hour, I appreciate your time (and patience).
Yeah, I do need to get some shuteye...

I'll check in tomorrow...

Let me leave you with this:

If the T T are ZERO it means that the Taco is telling the burner to fire.

If the T T is 24 VAC, it means that it is NOT telling to fire.

When ANY ZONE CALLS FROM THE TACO, it should tell the burner that heat is needed, meaning if any zone calls, you should see ZERO on the T T .

There COULD BE bad solder connections on the aquastat circuit board that may give FALSE INDICATIONS of the above.

Learn about DIFFERENTIAL control in the aquastat.

If the HIGH LIMIT is set at 180F, and your control has a 10F DIFFERENTIAL (not adjustable, built into control) it means that after hitting 180 and shutting off, it should fire again at 170F ... which is the HIGH LIMIT MINUS THE DIFF. (180-10)

If your high limit is set at 180, and the boiler is at 150, and any zone calls for heat, the burner should be firing.

Good Luck!
I'll check tomorrow.
 
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Old 12-19-13, 08:08 PM
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Here is my final report:

I have one zone calling for heat. Pumpis circulating but water temp is below 110 and the relay has not engaged/boiler not firing. I have 24v at T T. I also have 24v across the isolated end switch in the Taco panel.
 
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Old 12-19-13, 08:14 PM
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Tap on the relays in the TACO panel with a screwdriver handle.
 
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Old 12-19-13, 08:17 PM
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I have 24v at T T. I also have 24v across the isolated end switch in the Taco panel.
Which should be one and the same... so the WIRE is good, but the Taco is not telling the aquastat to pull in.

This would indicate a bad relay in Taco... but which one? the ENDSWITCH RELAY.

If you put jumper across TT or ENDSWITCH, relay should IMMEDIATELY pull in and burner should fire.

If it does NOT pull in immediately and fire, it ALSO means theres a problem in the aquastat.

OK, G'nite!
 
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Old 12-19-13, 08:18 PM
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You're good! It was like playing a piano, going down the keys - i hit one and the relay engaged; i hit another and it disengaged.
 
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Old 12-19-13, 08:23 PM
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You were a huge help. Thx again for your time! i owe you a beer - or five!
 
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Old 12-19-13, 09:00 PM
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Joy! I had a spare relay and replaced the one I believe is the endswitch. Furnace is running and I am hoping for this issue is closed. If I again wake up to a house that is <60 degrees, I will be back for guidance. Good forum, great advice. Many, many thanks NJ Trooper.
 
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Old 12-20-13, 04:40 PM
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Many, many thanks NJ Trooper
You're welcome!

i owe you a beer - or five!
OK, I'll drink to that! Out of the six pack, one for you, five for me!
 
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