Bench Testing Aquastat

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Old 12-09-12, 04:21 PM
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Bench Testing Aquastat

A couple of months ago I was having problems with my Honeywell L8148E1299 not starting the circulator pump unless I toggled the power switch or tapped on the top of the relay. It was suggested that I might have bad solder joint on the printed circuit board. The Aquastat was just under two years old. Since I was leaving town, I did not have time to mess with the Aquastat and the weather was getting cold. A new Aquastat solved the problem and now I have a defective spare that looks like new.

I would like to see if I can fix the old one and test it to see if it would work and I would like to do it on the bench. Now am I to look for a bad solder joint on one if the relay pins or what should I look for? If I find a loose connection and resolder it can I test it on the bench? I have a spare transformer with the proper power and a good multimeter and know how to use it. I am also familiar with AC circuits and their inherent danger.

It would seem to me that if I brought in 120 VAC to the Aquastat input terminals and if everything was working, I could jumper the thermostat terminals and measure voltage out to the boiler contacts and the pump contacts. Would that work?
 
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Old 12-09-12, 05:04 PM
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Now am I to look for a bad solder joint on one if the relay pins or what should I look for?
You're going to have the circuit board out of the aquastat, so inspect each and every solder joint with a bright light, and if yer over 40 a pair of 1.50 or better 'readers'. In fact, even if yer under 40, the readers will give you a better look.

For examples of what you will be looking for, go to Google and enter "cracked solder joint" and then click 'images' in the top bar... page after page after page of what you might find. Some are very subtle so examine carefully!

It would seem to me that if I brought in 120 VAC to the Aquastat input terminals and if everything was working, I could jumper the thermostat terminals and measure voltage out to the boiler contacts and the pump contacts. Would that work?
It should work.

I might put a 'load' on the C1 C2 terminals, such as a 60 W lamp.
 
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Old 12-10-12, 05:42 AM
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It could also be a bad relay.
If it's not a bad solder spot, the relay would be my next guess as it's really the only physically moving part in the aquastat.

If it was me, I'd simply replace the relay. This way, you've removed the potentially bad relay, and resoldered all the connections on it.
 
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Old 12-10-12, 07:33 AM
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Previously was the problem that the relay wouldn't pull in unless tapped? Or did the tapping help already-closed contacts?
Did you ever try to apply light pressure to the contact bar on top with a pencil to see if it will pull in? Sometimes light poking with a pencil point can can isolate the problem to the exact foil pad, loose wire or dirty contact.

Considering the simple wiring involved vs. the cost of replacement, I think a bench test is an excellent idea.
 
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Old 12-10-12, 02:48 PM
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I'd simply replace the relay.
IF you can find a plug and play replacement for it. I think it's entirely possible to be able to... and if it were, I would also search for an enclosed relay that can be socketed for future replacement.
 
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Old 12-10-12, 06:05 PM
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Where would I find a relay?
 
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Old 12-10-12, 06:30 PM
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Good question... it will be a difficult quest.

Many relays by different manufacturers follow the same "form, fit, and function".

If you can find ANY numbers or markings on the original relay, let me know and I'll do some looking.

The first thing is to try and identify the existing relay, then cross reference it to a part on the shelf at Digi-Key, Mouser, Newark, etc... parts suppliers.
 
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Old 12-10-12, 06:48 PM
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It says "Honeywell" on the top. On the base it has 131625MZMS 4 with a spot of white just after the 4. I think it is just the edge of a stamp pad. I googled "Honeywell 131625MZMS 4", but did not get a hit.
 
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Old 12-10-12, 07:07 PM
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The relays that Honeywell builds into these controllers are garbage. I would rather see you cannibalize the actual thermostatic switch from the controller and then build your own with a decent plug-in relay, control transformer and other components as necessary.

I have never used a stock aquastat for many reasons and chief among them is the lousy quality, but high cost of the standard units.
 
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Old 12-11-12, 09:14 AM
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I looked and looked and tried every single combination of numbers that you gave and was unable to come up with anything...

I'm SURE that a relay can be found that would work, the trick is that it is going to have to be a VISUAL matchup probably... which means having pictures of every relay ever made.
 

Last edited by NJT; 12-11-12 at 03:20 PM.
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Old 12-11-12, 07:28 PM
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Thanks for trying. I don't fully understand what Furd was suggesting, but I think if I remove the relay I might be able to figure it out. The relay has two contacts so I think it will be a DPST relay and the contacts will have to carry the voltage and amperage of the circulator. I don't think the relay controls the burner as it comes off the thermocouple. Do you have an idea of the amps coming off the thermostat which would be used to pull in the relay coil?
 
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Old 12-11-12, 07:51 PM
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One pole of the relay controls the circulator and the other pole of the relay controls the burner.

The thermocouple is only a signal to the gas valve that the pilot is lit and it's OK to open the main valve. Pilot goes out, thermocouple goes cold, gas valve won't open no matter what.

amps coming off the thermostat
The thermostat side of that circuit is only a few hundred MILLIamps, not much current at all.
 
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Old 12-12-12, 12:44 PM
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I misspoke. I was not referring to the pilot light thermocouple, but the sensor going into the boiler well. So when my relay was turning on the boiler and not the pump, that tells me the relay coil is working, so it is either the pump relay contacts or the output solder connections to the pump circuit. Am I correct?
 
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Old 12-12-12, 02:23 PM
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relay was turning on the boiler and not the pump, that tells me the relay coil is working, so it is either the pump relay contacts or the output solder connections to the pump circuit. Am I correct?
Yes, that would be my guess.
 
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Old 12-17-12, 07:43 PM
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I could not find a relay that would be a direct sub so I found a socket type relay and removed the circuit board relay. After removing the relay I soldered 6 wires onto the circuit board and ran them to the relay socket. The relay will be mounted in a separate box on the side of the aquastat. Now if the relay fails I can just pop a new in the socket.

The relay is an Allen Bradley 700-HA32A24. I picked mine up locally, but they can be purchased on the internet for under $20. The AB relay is much more solid than the original and I don't expect it to fail. Beats spending $165 or more for a new aquastat.

If anyone needs more information or pictures, let me know.
 
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Old 12-17-12, 07:53 PM
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I'd like to see your work! yes, pics please!
 
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Old 12-18-12, 10:12 AM
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Sounds like a good solution! IMO always better to fix a simple problem rather than toss it in the landfill
Did you ever determine if the problem was the coil not pulling in the contacts, the contacts not "making", or bad connection on the circuit board?
 
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Old 12-18-12, 01:20 PM
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I only scanned this thread, so I may not have the complete picture. But gas valves normally operate on the 24V control voltage and draw little amperage, thus no need for a relay such as for a circulator pump that runs on 120V. (My 24-V gas valve draws 0.2A.)

I share Furd's disdain for the relays (and also transformers) packaged inside of Honeywell (and probably other manufacturers) residential-grade control equipment. Industrial users wouldn't stand for it.
 
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Old 12-18-12, 03:30 PM
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The coil worked fine. The contacts were not functioning.
 
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Old 12-18-12, 03:34 PM
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The relay has two sets of contacts. One set controls the burner. The other controls the circulator pump which is 120 Volts. Some run the circulator continuously; therefore not needing a relay.
 
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Old 12-18-12, 03:39 PM
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I will send pictures later. Have to prepare for a blizzard right now.
 
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Old 12-18-12, 03:46 PM
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Some run the circulator continuously; therefore not needing a relay.
Can you elaborate? I'm uncertain why one would run the circulator continuously.

But my question was why have a relay for the 24-V gas valve?
 
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Old 12-18-12, 04:12 PM
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But my question was why have a relay for the 24-V gas valve?
How else would you control the valve?
 
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Old 12-18-12, 04:48 PM
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How else would you control the valve?
Directly from the 24-V control voltage through the thermostat and/or an aquastat (depending upon whether warm start or cold start). No relay necessary for a 24-V fuel valve. What would you do with a relay? 24V to the coil and then 24V again on the contacts? Why?
 
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Old 12-18-12, 05:39 PM
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Why?
Thermostat wired to aquastat to control relay that turns on/off 120VAC circ.

Same relay also turns on/off 24VAC gas valve on second pole.
 
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Old 12-18-12, 07:23 PM
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If you use the thermostat to control the gas valve you would be running the boiler all the time and it would over heat. You need to go through the aquastat and therefore the relay to control the boiler heat cycle.
 
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Old 12-19-12, 10:00 AM
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Originally Posted by hhornig

The coil worked fine. The contacts were not functioning.
...unless you cycled the power or tapped on them, if I recall. Did you ever try cleaning the contacts? Might just be some pitting or corrosion? It may happen again to your new relay as well--but being sealed you won't have the option of cleaning the contacts.
 
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Old 12-19-12, 10:30 AM
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Here's the way my warm-start boiler is set up: aquastat controls the burner, supplying 24V to the gas valve on make. No relay involved.

The thermostat controls the circulator through a relay.
 
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Old 12-19-12, 04:23 PM
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Yes I tried to clean the contacts. I even tried to file them with a point file after the cleaning failed. The replacement relay has much larger contacts and just plugging in a new relay will be nice.
 
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Old 12-19-12, 04:26 PM
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What kind of aquastat do you have?
 
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