Leaking Pressure/Temperature Relief Valve


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Old 03-12-09, 06:19 PM
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Leaking Pressure/Temperature Relief Valve

Hello,

I just purchased a home with a natural gas water baseboard heat system. Since I've moved in the home, it's been my opinion that the boiler cycles on and off too often.

I noticed some operating parameters that seem out of the ordinary. According to the temperature/pressure gauge on the pipe label labeled "to system", the boiler cycle between 140F and 170F; the flame ignites at 140F and turns off at 170F. The pressure needle on the guage does not work... it's reading below zero PSI. The problem I noticed is that once the temperature reaches about 150F, the pressure/temperature relief valve on the top of the boiler tank begins to leak. I'm assuming this is not normal operation, correct?

The unit is a Weil-McLain Gold GV. It was installed in 1993. How long do units such as this one usually last?

This is what the unit looks like:


Thanks,
Rich
 
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Old 03-13-09, 03:28 PM
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Rich, first things first, you've gotta know the pressure in the system. So, you've either gotta replace the gauge, or improvise an 'external' pressure gauge. I always post this pic of my junque boxe model, but nicer ones can be made... or bought...



Screw this thing onto a drain, open it, and read the pressure.

Does your home have a separate hot water heater? or does the hot water come from the boiler?

If you feel adventurous, see that gray box on the side of the boiler? That's your 'aquastat'. There should be one small screw holding the cover on. Turn the emergency switch to the boiler off, loosen that screw and slide the cover off. There should be a label inside... what is the model # of that box?

Next, what type of 'expansion tank' do you have? Is it the type that looks like a gas tank from a grill? or is it a bigger steel one that's strapped into the ceiling joists above the boiler?
 
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Old 03-13-09, 04:37 PM
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Thanks NJ Trooper!

I'll get a new pressure guage soon, but for now I'll try to rig something up this weekend.

I just wanted to provide a little more information about the system.

The hot water tank is fed from the boiler. It's a Amtrol WH-7.

The backflow preventer is a No9D.

The reducing valve is a ITT Bell & Gossett model B7-12. (I think... there's a scratch on the label and I'm not positive it's a 7 in the model #.)

The expansion tank is of the propane tank looking variety. It's a Amtrol Extrol model #30.

If I'm looking at what you're referring to as the 'aquastat', I don't think that's it. That is just a metal j-box where the 110v power comes to the boiler unit. Between the 110v power switch and that gray box, there is a black box labeled "McDonnell Level Control - ITT McDonnell & Miller." The flexible conduit runs to this box from the shutoff switch and then to the gray j-box mounted to the side of the boiler housing. The "from system" water line also runs to this box. Is this the aquastat?

Thanks again for your help.
 
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Old 03-13-09, 05:04 PM
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I just re-acquainted myself with your boiler... can you tell the 'series' number of the boiler? What's it say on the ID plate? You don't have the 'aquastat' I mentioned... there's a 'control module' in that boiler.

Offhand, it sounds as though your expansion tank is either very low on air, or has a ruptured bladder. When the water hits 150 degrees, the pressure is up around 30, and the relief valve opens.

Is there a shutoff valve in the line between the boiler and the expansion tank? or is it piped directly?

You need to shut off the boiler, close the manual feedwater valve, and open a drain on the boiler to get the system pressure to ZERO (but you won't know till you get a gauge!), and using an accurate tire pressure gauge on the tank air fitting, check to see that you have 12-15 PSI air charge. If the tank air fitting is pointing DOWN, and you get WATER out of that air valve, you need a new tank. If you don't get water, use a bicycle pump or small air compressor and put 15 PSI in the tank. Then, reopen the manual valve and repressurize the system. Turn the boiler back on and you should be good to go.

NOTE! Do NOT drain any more water than you need to in order to drop the pressure to zero. The less water you change, the better.
 
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Old 03-13-09, 05:07 PM
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The hot water tank is fed from the boiler. It's a Amtrol WH-7.
That means you have what is called an 'indirect' water heater.
 
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Old 03-13-09, 10:39 PM
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Originally Posted by NJ Trooper View Post
That means you have what is called an 'indirect' water heater.
Thanks... I would really like to get fairly familliar with this system, so I apologize for the numerous questions. I was kind of wondering why the hot water tank says "Residential Hot Water Maker" on it when it doesn't really "make" any hot water... isn't it just more of a storage tank? Is an indirect water heater generally preferred over a standalone water heater? It seems it has some advantages, but one disadvantage is that I can't take the whole system down and still take a hot shower.

Originally Posted by NJ Trooper
... can you tell the 'series' number of the boiler? What's it say on the ID plate?
The boiler is a model GU-4 Series 2.

Originally Posted by NJ Trooer
Is there a shutoff valve in the line between the boiler and the expansion tank? or is it piped directly?
There is a shutoff valve and a drain valve. The expansion tank is connected to and suspended by the pipe above it with the schraeder valve on the bottom.

Originally Posted by NJ Trooper
...close the manual feedwater valve...
Is this the valve that supplys the system with city water?

Originally Posted by NJ Trooper
...and open a drain on the boiler to get the system pressure to ZERO (but you won't know till you get a gauge!)
How will I know it's safe to unthread the current broken gauge w/o knowing the pressure in the system? Shall I drain it a bit and then just unthread the gauge slowly and carefully?

Originally Posted by NJ Trooper
NOTE! Do NOT drain any more water than you need to in order to drop the pressure to zero. The less water you change, the better.
Is the reason for this just so the system only has to reheat as little new water as possible or are there other reasons that you don't want to introduce a lot of new water to the system? I just bought this house and I'm not really sure how long it's been leaking, but by the looks of the concrete around the boiler, it's been a while... that leads me to believe that it's efficiency is being severely compromised because of all the wasted hot water.

Also, I know nothing about the name brands I'm dealing with... i.e. Weil McLain, Amtrol, ITT, etc... Are these reputable brands and how do they rank overall? Are they like a Yugo or a Bentley?

I took a bunch of pictures of the system, but unfortunately I just moved in to this house and can't find the cable for my camera!

Thanks again,
Rich
 
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Old 03-14-09, 01:52 AM
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isn't it just more of a storage tank? Is an indirect water heater generally preferred over a standalone water heater?
It is a storage tank. There is a coil of pipe inside through which the boiler water passes and heats the water in the tank. Indirects are very efficient in general, and one less 'burner' to maintain. WAY better than an electric (depending on your electric rates... cheap hydro sometimes is cheaper to run an electric)

The boiler is a model GU-4 Series 2.
Is that GU a typo? Did you mean GV?
That's an 'older' one then... I believe that your boiler has one pump internally, and also a 'mixing valve'... the series 3 and newer have replaced the mixing valve with a second pump. You can download the manual from the Weil-Mclain website if you don't have it.

There is a shutoff valve and a drain valve.
Is the drain valve in between the tank and the shutoff valve? If so, the job of checking/adjusting the air charge gets a LOT easier! You don't have to drain the pressure from the boiler if it's set up this way. Simply close the shutoff valve to the tank, hose on the drain, open drain and let water pressure off the tank. Leave drain open for now, check/adjust pressure, then close drain, and slowly open shutoff. Done. Bottom line is that you need the 'water' side of the tank to be at atmospheric pressure in order to get an accurate check/charge of the pressure on the air side.

Is this the valve that supplys the system with city water?
Yes, and 'downstream' of that, toward the boiler should be a 'pressure reducing valve' that regulates the city water pressure down to the boiler pressure. There should also be a 'backflow preventer' in that line.

How will I know it's safe to unthread the current broken gauge w/o knowing the pressure in the system? Shall I drain it a bit and then just unthread the gauge slowly and carefully?
This gets a little trickier... if you hook up a drain hose to one of the drain valves, you will pretty much know when there's no pressure in the system... flow will slow/stop... BUT... when replacing the gauge, you may have to drain a bit out unless you work real fast... even then, you will spill some water... and you should look around for valves on the pipes that you can close to 'isolate' sections so that you only have to drain a minimum amount of water...

Is the reason for this just so the system only has to reheat as little new water as possible or are there other reasons that you don't want to introduce a lot of new water to the system?
The main reason is that fresh water has lots of oxygen entrained in it... your old nasty boiler water does not. Oxygen is what causes rust and corrosion. If you add lots of fresh water, when that water is first heated, you get lots of air running around in the system and it can be a pain to get it all back out again. Obviously in some cases you have to drain water to service, but the idea is to keep it to a minimum. The water in boiler systems does not need to be changed, it's best to just leave it be.

A long term leak will constantly add oxygen to the system and will cause faster corrosion to the parts... also, minerals in the water will build up inside.

Hunt down that cable... so much easier with pics so we can tell you which valves to turn...
 
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Old 03-14-09, 12:05 PM
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That's an overall photo of the system, and I think the link below should take you to the album w/ more detailed photos.

Boiler pictures by bajafx4 - Photobucket
 
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Old 03-14-09, 12:12 PM
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Originally Posted by NJ Trooper
It is a storage tank. There is a coil of pipe inside through which the boiler water passes and heats the water in the tank.
That now makes sense of why the hot water tank has 4 water pipes going to/from it.

Originally Posted by NJ Trooper
Is the drain valve in between the tank and the shutoff valve?
Yes the drain is between the expansion tank and the shutoff valve.

We're going to a birthday party right now and my wife is waiting at the door for me. HA! Or else I go down and check to see if that model number is GU or GV. I do remember for sure that there's a company label on the boiler from the installer that says they installed the system in 1993 if that helps.

Gotta go,
Rich
 
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Old 03-15-09, 08:09 AM
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Rich, there's no drain or valve that I can see between the system and the expansion tank. What I meant was something like this:



Setup like this, and you can isolate the expansion tank and drain the pressure from only the tank. Otherwise, you still have to relieve the pressure from your system as I first described.

4 pipes into water heater:

Yes, the water heater is for all intents another 'zone' on the heating system. When it cools, the control on the water heater calls the boiler just as a zone thermostat would do.

BTW, I added a few comments to your pics...
 
 

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