How to troubleshoot possibly bad aquastat? Get's stuck on. Replacement PN?

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Old 03-12-11, 08:56 AM
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How to troubleshoot possibly bad aquastat? Get's stuck on. Replacement PN?

I am experience issues where say, 1 out of 5 times, my heat stays on, even though the thermostat sends the 'don't stay on!' signal. I can wake up in the AM and it be 80 degrees.

I thought it was possibly the thermostat and/or the thermostat wire since the wire was pretty shotty, so I replaced the thermostat wire, and no dice.

I took the thermostat out of the equation and just manually connected and disconnected the two little thermostat wires together a few times, and low and behold after a few times, I separated the wires, and everything stayed on.

The circulator pump is definitely staying on, and I'm 'assuming' the furnace is still firing as, the house keeps getting hotter. I'm 99% sure it's the aquastat, (has to be right?)

Here is a photo of my setup. It's a White Rodgers 8F42A






I've googled around a bit but can't find a cross reference or replacement part number.

Also, what are the appropriate replacement procedures? Do I have to drain the system?

Thanks!! It's driving me nuts. If there are any other 'tests' I can run or any other fixes I'm all ears!
 
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Old 03-12-11, 12:33 PM
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From you post I would say you may have some things to look at.

1) The boiler may just be coming on because its below temp. It will do this to keep the boiler warm regardless of what the t stat says.
2) If the above is true, and your heat emitters are getting hot, then there is a flow control issue. ( not enough visual in the pic to make a conclusion)
3) The other thing is when the boiler shuts down what does the temp say on the boiler? It should cut off at 180F or so. If indeed the aquastat was faulty the boiler would just keep running until the releif valve blew off from overheat.

Take more pics of your system. Give us more detail about temp and pressure at the boiler gauge. Zones? Type of heat emitters.

Mike NJ
 
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Old 03-12-11, 01:36 PM
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It will do this to keep the boiler warm regardless of what the t stat says.
But I don't see any evidence that this is a 'triple' aquastat? All I see is a single high limit control... Nor do I see a domestic hot water coil... I don't think this is part of the issue...

Murph, have you got a stand alone water heater for the domestic hot water?

manually connected and disconnected the two little thermostat wires together a few times, and low and behold after a few times, I separated the wires, and everything stayed on.
This sounds as though the relay in the aquastat is 'sticking' on...

As for a replacement, it might take a little research... I'll look later on this evening see what I can find out.

Do I have to drain the system?
Rarely... probably not.
 
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Old 03-12-11, 01:38 PM
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Murph, have you got a multimeter and know how to use it?
 
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Old 03-12-11, 01:46 PM
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I do have a multimeter. As for using it....I can surely take readouts, without knowing a damn thing they might very well mean!

I have a separate hot water heater. This is a very small house, very simple unit. You are correct when saying it's just a single high limit control.

And yeah, seems like the relay is just sticking. I hear the thermostat click, and usually I hear the circulator pump click off, but when it sticks, the pump still runs and the house gets much hotter so I'm assuming that the boiler is continuing to fire. I think the thermostat in the aquastat (say that 10x fast) is working and controlling the calls to the furnace just fine as the heat has stuck on for a whole weekend and no pressure valve exploded....
 
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Old 03-12-11, 09:53 PM
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Sorry I didn't have time to research your a'stat... I'll look tomorrow...

How do you get it to 'unstick' when it's stuck? Does a little 'tap' on the aquastat do it?

That part with the '775' on it is the relay. When it's stuck, you may be able to visually see that the contacts are together.

Is there any way to get a picture of the back of the aquastat where it's mounted to the boiler? maybe with a mirror? It would help to see that to know if a Honeywell will replace yours. I'm thinking (hoping) that a version of the 8148 would match up...

You _might_ have to drain, if the honeywell replacement doesn't fit on your 'immersion well' ... but let's hope for an easy fix.
 
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Old 03-12-11, 10:01 PM
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I lied... I just looked it up:

8F42A-5 WHITE RODGERS / HONEYWELL FUNCTIONAL REPLACEMENT L8148J1009

When Honeywell says 'Functional replacement' it could possibly mean that you have to change the immersion well (the part that the sensing bulb slides into, and the aquastat clamps onto) ... but you also might be able to use the adapter that should come with the aquastat.

Here's a source for it:

L8148J1009 - Honeywell L8148J1009 - Aquastat Relay

Here's the install manual from Honeywell:

http://customer.honeywell.com/techli...0s/60-2278.pdf

Be sure to note that the replacement aquastat will work with EITHER a 24VAC gas valve, or a MILLIVOLT gas valve. Make sure that you use the correct terminals when you wire the burner to it.
 
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Old 03-13-11, 12:23 PM
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Thanks for the info. I'll go see if I can get some pictures of behind the a'stat.

When it sticks, to get it unstuck, I just turn the thermo up, wait for it to click on, then turn it down low, and wait for it to click off, once is enough to get it to trip.

When it is stuck, yeah the contacts on the relay are together.
 
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Old 03-13-11, 12:41 PM
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Ok...


heregoes.

fromunda:


From side:


valve:


beast:


Appreciate the effort and the info.
 
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Old 03-13-11, 03:32 PM
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Aquastat or Thermostat?

From what you are saying about turning the thermostat up & down makes me wonder if the thermostat isn't the problem. Next time the aquastat sticks, disconnect one of the thermostat wires at the aquastat.
 
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Old 03-13-11, 03:53 PM
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Did that in le first post.
 
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Old 03-13-11, 08:30 PM
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Sorry Murph. I looked at the words but they just didn't register.
It looks like you would loosen the screws on the bracket where the capillary goes thru the aquastat in order to remove the aquastat from the well. The Honeywell will likely clamp right on the well.
 
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Old 03-17-11, 08:28 AM
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Thanks guys, ordered that replacement, let's hope I'm not back on here scratching my head begging for help!
 
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Old 03-17-11, 09:23 AM
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S'OK if ya do come back... we're here for ya!
 
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