Gas-fired hot water system will not turn off

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Old 12-16-12, 09:44 AM
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Gas-fired hot water system will not turn off

A couple weeks ago I noticed that it was way too hot in our house. Since that time, I've had to use the furnace kill switch on the wall to make the circulator stop running.

My system consists of a Slant Fin Galaxy 75,000 BTU gas-fired boiler (manufacture date 1991) with one circulator pump and two zones with Taco zone valves. I currently have digital programmable thermostats on both zones with batteries that are less than one month old for the basement and 2 days old for the first floor. Here is what the furnace wiring looks like: Furnace - Imgur

When this first happened, I didn't do a lot of troubleshooting. I figured the 1st floor zone valve looked old, so I bought a new head to replace it. I replaced the other zone valve when I bought the house 5 years ago. That didn't fix the problem, so I then figured instead of calling a professional, I'd spend $200 on a new Honeywell Aquastat L8148e. That also did not solve the problem. I then decided I needed to do actual trouble shooting.

The new aquastat came with a wiring diagram, of course, so I unhooked all of the wires between the power source, thermostats, zone valves, and aquastat. I believe they were correct in the first place, but they were really messy. They are still messy, but I'm quite certain that I hooked everything up correctly.

Now the troubleshooting: With the main power on and with the furnace in "resting" position, I have 24 volts between terminals 2 and 3 on both zone valves. When I call for heat on either one or both of the thermostats, I then have 24 volts on terminals 1 and 2 of the corresponding zone valve. Terminals 2 and 3 retain 24 volts for a minute or less and then goes to zero, at which point the circulator turns on and the boiler fires up, if required. Prior to the boiler firing up, the damper automatically opens. When the requested air temperature is reached, the thermostat clicks off, voltage returns to zero on terminals 1 and 2, and the circulator stays on indefinitely. I'm not sure what is supposed to send the 24 volts to terminals 2 and 3 to shut off the circulator, but it is not typically happening. During my troubleshooting I've had a few occasions where 24 volts went back to terminals 2 and 3 thereby shutting the circulator off, but that has only served to confuse me further.

If anyone has any advice or other things for me to check, I would appreciate the feedback. This is my last attempt to fix this myself before I call a professional. I'm lucky in that I DO have heat, it's just a pain in the butt to keep using the wall kill switch.

Oh, one more thing to add, when I do use the kill switch and leave it off for an extended period of time (maybe an hour or so), when I turn it back on, 24 volts is back on terminals 2 and 3. The furnace then just sits there at rest until heat is called for again.

Matt
 
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Old 12-16-12, 09:58 AM
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Your zone valves have a microswitch in them so that when they are open (calling for heat) that switch closes and tells the aquastat you need the pump to run and additional boiler temp.

It sounds like one of your zone valves is sticking open.
 
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Old 12-16-12, 10:15 AM
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Is there any way to unstick it other than replace the valve body?
 
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Old 12-16-12, 10:52 AM
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Also, I would like to say that your response makes a ton of sense, because when heat is called for in my basement, the circulator turns off like it should. In addition to that, I pulled the valve head off the upstairs zone, and there is water on top of the valve body. I really don't want to drain the system and replace the body, but I guess that's what I'm looking at now that I see it's leaking.
 
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Old 12-16-12, 11:23 AM
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Not much time right now, but the drawing that PJ posted is typical of the Honeywell 'type' of valve. The Taco which you have has only three terminals, I'll post the typical Taco setup later and talk about the sequence of operation and the endswitches, etc...
 
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Old 12-16-12, 11:37 AM
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No way of unsticking other than changing. Usually the packing leaks and then it sticks due to the corrosion.

Yeah....I posted the quickie honeywell pic. On your Taco valves # 3 is the output to the aquastat. So you could disconnect one at a time and you'll know which one for sure is causing the issue.

On edit: just re-reading your last post. Seems the basement zone works fine but the upstairs one (with leak) is the culprit.
 
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Old 12-16-12, 01:26 PM
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Here's the basic Taco wiring:



Sorry not great quality, but readable.

Note that 2 and 3 will be connected in parallel on all valves, thus PJ's suggestion to remove the wire on terminal 3 , one at a time, until you find the one that is stuck open. With them all in parallel, you will never be able to tell which is faulting.

Between terms 2 and 3 on the zone valve is a SWITCH. This switch closes when the valve opens, and it SHOULD do vice versa. It does sound as though one is intermittently hanging up.

thermostat clicks off, voltage returns to zero on terminals 1 and 2, and the circulator stays on indefinitely. I'm not sure what is supposed to send the 24 volts to terminals 2 and 3 to shut off the circulator, but it is not typically happening.
Nothing really 'sends' 24 VAC to terms 2 and 3. What you are seeing there is the control voltage coming out of the boiler control (aquastat).

When the switch in the zone valve is OPEN (the VALVE is CLOSED), you will read 24VAC. When the switch CLOSES, (Valve OPEN) you will be reading across a closed switch, a short circuit... thus you won't read a volatge.

Hope this makes sense...

So, yes, next time it hangs up, remove wire from terminal 3, one at a time, until you find the stuck open valve.
 
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