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Does this sound like an a’stat relay problem?

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  #1  
Old 12-04-12, 06:21 PM
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Does this sound like an a’stat relay problem?

hi folks -

My boiler system has 2 zones each with a Taco 007-F4 pump.
Aquastat is L7224U with C1 -C2 connected to the zone 1 pump, and ZC -ZR connected to an R845a relay for Zone 2. I have a programmable thermostat for each zone that displays “Heat On” when it calls for heat.

Two days ago it felt cold in zone 1. Zone 1 thermostat showed “Heat On”.

At the L7224U the display showed:

Boiler temp = 182
Burner= OFF
Cir = ON

It sounded unusually noisy in the L7224U box. The return pipe from Zone 1 was cold even though the L7224U display showed Cir = ON. So I figured either the zone 1 pump was bad or the C1 relay was not really closed. Not smart, but I powered off the system and then powered it back on without first checking voltage across C1-C2.

For some reason after power back on the burner came on even though boiler temp (182) was near the high limit (185)? Cir according to display was still ON. Boiler water temp started to drop as water circulated and zone 1 warmed up and the burner came on/off in a normal cycle and eventually the zone 1 t’stat was satisfied. Thus it seems that powering off then on corrected the problem.

Later that day problem reoccurred. This time I checked the voltage across C1-C2. Set meter (digital) to read 120 volts but got some error indication on the meter when checking C1-C2. (Didn’t have my manual handy then but red LED was flashing, main display flashing? Probably operator error.)

But anyway, I then smacked the L7224U up side its head and what do you know, I heard what sounded like a rush of water and all of sudden the water started to circulate through zone 1 and the heating cycle completed as normal.

Later that day I checked C1-C2 with the meter and got 115 volts when the zone 1 circulator was running.

I checked all the wiring in the L7224U and couldn’t find any loose or bad connections. Everything looks OK?

So what I’m asking is, doesn’t this obviously point to an intermittent relay problem in the L7224U? And if this problem persists is it time for a new L7224U? I know how to do that because I put this one in a little over 4 years ago. Not a bad job, even I can do that.LOL

Any thoughts would be greatly appreciated!
 
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Old 12-04-12, 06:30 PM
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So what I’m asking is, doesn’t this obviously point to an intermittent relay problem in the L7224U? And if this problem persists is it time for a new L7224U?
Zoe it absolutly sounds that way. More so because you smacked it upside its head.......LOL

Wait for the others to chime in but I would lean towards the relay.

Oh and very thorough in you diagnostic....


 
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Old 12-04-12, 06:32 PM
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thanks Mike!

p.s. it was a precision smack.LOL
 
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Old 12-05-12, 09:50 AM
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Just thought I’d post this and will update in the future because it may help someone else to see what the frequency of this type of problem might be.

Problem hasn’t happened again? But I know it happened twice in one day and I didn’t jump the gun. For sure the zone 1 pump was not pumping. Gremlins? LOL
 
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Old 12-05-12, 03:28 PM
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I'm not happy that a four year old a'stat acted up like that... not happy at all. Shakes my faith in electronics made in Mexico... (that's my guess). Not that I ever had any... let alone faith in electronics made in the US these days.

If it were mine I'd be getting out my lighted magnifying inspection goggles and give it a good once over looking for bad solder. I HATE SURFACE MOUNT! Just last week I helped one of our techs troubleshoot a device that we build. Six years old... (the device, not the tech, although he acts it! I think he learned it from me!) and it worked fine up to this point.

Finally I found the problem. One of the small surface mount resistors had never been soldered to it's pad. All those six years it was just 'touching'. A little touch of solder and all was well again in Whoville.

This story simply to illustrate the point about that dang surface mount stuff.
 
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Old 12-05-12, 05:14 PM
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...If it were mine I'd be getting out my lighted magnifying inspection goggles and give it a good once over looking for bad solder...
Trooper that is exactly what I was thinking. It seems to me that would be a good educational exercise for me at least. I never tried an inspection like that before but it seems to me it would be a good training experience for me at least. If I find anything I’ll post back.

I HATE SURFACE MOUNT!
I didn’t even think of that! Obviously my electronics training is lacking.LOL

Thanks!
 
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Old 12-11-12, 10:26 AM
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hi folks -

I just wanted to post in case this helps someone evaluating potential problem causes. The problem has not repeated? The circulator for zone 1 runs as expected. It almost seems as if it was just that one day, and 2x that day?

As Trooper suggested I did give the surface of the board a good look with my good glasses and a magnifying glass. I don’t see anything that jumps out at me, but maybe the obvious might not jump out at me? LOL

I know I did NOT make a mistake, that circulator was NOT running when the L7224 said it was. Powering the entire system off then on immediately started it the one time. The next time I got rough with the L7224 (smack!!!) and showed it who’s boss and the circulator started immediately.

I’ll post back if there is anything helpful to say.

Thanks!
 
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Old 12-11-12, 03:00 PM
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Keep us posted... it is an interesting case!
 
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Old 12-11-12, 03:08 PM
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Surface mount look for a uniform joint.




I did my share of soldering when working for Lucent Technologies.

I like surface mount better... Just me though....
 
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Old 12-11-12, 03:32 PM
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I like surface mount better... Just me though....
Yeah, just you! ha ha ha

Me: IPC certified, all technologies.

If I was younger, like you, and my eyes weren't failing me, I might like it too.
 
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Old 12-11-12, 05:45 PM
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Thanks Mike. Those are great pictures. I think maybe I can do a better job when I re-inspect.
 
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Old 12-15-12, 11:02 AM
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Thought this might be helpful to someone:

Wouldn’t you know it? I swear, the very day I made that last post (#7) the L7224 acted up again. This time the problem was not intermittent. I could check C1-C2 and would get zero volts until I continued to tap the L7724. The relay would then close (I guess), I would then get 115 volts and the circulator would then run. Had to repeat this each time to get the zone heated.

Hope this is OK to plug Patriot-Supply but I think this might help others? I ordered a new L7224 from Patriot-Supply late last Wednesday afternoon and I was shocked to find it in my driveway Thursday afternoon. Came standard UPS. (But I’m in Pa. and they are in New York not too far away. I guess that matters.)

They also had the best price around. (I’ve also ordered some other things from Patriot-Supply and they are very fast and have very good prices.) Put the L7224 in the day it arrived and everything is fine. I used Mike’s great pictures to see if I can see anything that looks soldered improperly on the bad L7224. If something is wrong I can’t see it.

So maybe the moral is if your relay(s) in your control start to act up, fix it, because it’s only a matter of time before it’s totally useless and it could be at the most inopportune time? LOL. Or something like that.LOL
 
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