"Superstore" 40 gal hot water tank discharging through overflow - why?

[McG]

We were away for a few days and shut off the oil burner/boiler (Weil-McClean Gold) while we were gone. We turned the boiler on when we got home. A day after returning home I heard water running in the cellar - the overflow from the Superstore was discharging into the one gallon pale on the floor and overflowing. The cellar floor was soaked. I flipped the spring loaded pressure release valve at the top of the discharge pipe and the discharge opened up full force. Releasing the valve did not return the flow to a strong trickle instead it was a stronger flow. Finally I turned off the cold water feeding the tank and shut off the boiler. What's going on and how do I correct the problem?

[jadnashua]

I'm assuming that the place where it was leaking was the T&P valve?

That is designed to release under any one of two conditions: excessive pressure, or excessive temperature. Weeping a little is likely if the expansion tank is shot (or there's none installed). But, a strong flow is not normal. What was the temperature of the water being discharged?

If I had to guess, I'd guess that your expansion tank is shot and the T&P valve has some mineral deposits on it, and once it tripped, it wouldn't reseat. So, I'd check the expansion tank, and then replace the T&P valve unless the boiler was running away, and the tank was excessively hot.

It's possible, if you have excessively high water pressure, that your PRV is shot. You should also check the incoming water pressure to rule that out.

[McG]

Thanks. The temperature of the discharge is not excessively high. Yes, I believe it is the Temperature and Pressure Relief valve. And yes, I have a very old expansion tank, shaped like a half barrel and attached to the ceiling between two floor joists. The fella who installed the boiler said the old expansion tanks were better than the new ones and never need replacing because there's no bladder to fail. Anyway, he left it. Two years ago, a year after the installation, I called him and he drained my expansion tank after tapping on it and saying it will full. I assume an expansion tank must be capable of filling and emptying itself. Would you recommend I drain the expansion tank as a plan A to resolving the problem?

Your reply synopsizes what I found described on this web page http://www.factsfacts.com/MyHomeRepa...sureRelief.htm

2 hours later --
I drained the expansion tank, collecting 20 gallons of water. I turned off the feed before opening the drain. I had to blow into the hose to release air locks, kind of like blowing into a straw immersed in a bottle of soda. After gurgling in the tank, water flowed again slowing to a trickle. But this expansion tank does not interface with the hot water storage tank. The cold water in and the hot water out do not pass connect with the expansion tank at any point.

I opened the cold water-in line to the storage tank and immediately water gushed from the relief valve pipe. Flipping the valve up and down had little effect. Does this mean I have to replace the valve? It is only three years old, same as the boiler and tank.

[jadnashua]

A home might have a couple of expansion tanks, one if it has a boiler, and a second one for the WH. The old style tanks eventually fill up with water, so they require periodic maintenance. The newer bladder styles work until the bladder dies, then you replace it. I'd rather have it work like a switch until it fails than require periodic maintenance.

If things are cold and the pressure isn't exceedingly high, then yes, the T&P valve probably needs to be replaced.

[McG]

House PSI is 79. Bought Watts Det-5 expansion tank. Max precharge is 80psi (79 is awfully close to 80). Bought new T&P valve for Superstore. Ready to install? I learned there is no airscoop on the boiler. Maybe we don't need one with the old fashioned expansion tank. Don't know. There is no pressure reducing valve, or backflow preventer on the cold water inlet to the WH. It may be obvious to those who know - but which line of the WH does the expansion tank go on, the cold water inlet or the hot water outlet?

[jadnashua]

Potable water expansion tanks are designed for COLD water use only. One designed for a boiler, obviously, needs to work on the hot side, but is NOT rated for potable use.

An expansion tank is ONLY required when there is a closed system. That is almost always the case on a boiler, and is true on the potable water system if there is a check valve or a PRV in the system. So, if the expansion tank is for the boiler, then it should be rated for hot water use, and sized for the volume of hot water inside of the boiler and heating runs. If it is for the WH, then it should be sized for the volume of the tank and the normal temperature rise.

A boiler operating pressure is normally only in the 12-20# range (could be higher, depending on system design and building height).

PRV will normally be on a WH and another one on the boiler. They have different ratings for pressure and temperature, normally. Make sure to match the type and ratings when replacing.

There are normally things that can corrode in a boiler...air (oxygen) in the water makes it happen. If there's none, it generally stops. So, a means to extract that air is generally a good thing, but on a good system, there may not be much. You WILL have some when you first fill the system, and any time you need to add water, it will likely contain some air as well. A pump might create a vacuum, and suck some in, if there is a leak, or the act of heating and cooling the water will generate a change in pressure that can do it.

[McG]

Jim, the Watts Det-5 expansion tank is for the Superstore Delta 40 gallon indirect water heater. The old barrel expansion tank is for the boiler. I assume the water in the WH that is spilling out of the Superstore T&P valve will now back up into the expansion tank even though the Det-5 is installed on the cold water inlet to the tank. Is 78psi as the supply water pressure excessively high? I have been calling the city water department all day but no one answers the phone there - just voice mail.

[Redwood]

Pressure above 80 psi incoming water pressure would call for the installation of a pressure reducing valve.

Pressures may be higher at different times of the day and night. Using a lazy hand gauge to record the highest pressure over a 24 hour period is recommended when checking water pressure.

[McG]

Where in the system would I install a pressure reducing valve, Red? Is the high supply pressure causing the discharge at the T&P valve?

I have finally read some of the literature from the manufacturer of the Superstor Ultra (not Delta as I've been calling it) Indirect WH.

EXPANSION TANK
"A thermal expansion tank may be required in the system designed for potable water use, to
offset the expansion of stored water as the temperature is elevated (only in systems where
there is a no return valve, a back flow preventer, a water meter, or anywhere pressure can
build up as the water is heated)."

There is a backflow preventer on the boiler and there may be one in the city's water meter at the service entrance but on the WH, there is none. So, I wonder, did I really need the expansion tank on the water heater?

This from the Superstor Ultra installation trouble shooting page:

T&P VALVE DISCHARGES:

PROBLEM: POSSIBLE SOLUTION
A. ZONE VALVE RESTRICTION A. 1" FULL BORE REPLACE ZONE VALVE
B. CIRCULATOR ARROW REVERSED B. REVERSE CIRCULATOR
C. TANK TEMPERATURE TOO LOW C. RAISE TANK TEMPERATURE (SEE WARNING THIS SECTION)
D. BOILER TEMPERATURE TOO LOW D. RAISE BOILER TEMPERATURE
E. BOILER SIZED TOO SMALL E. CHECK SIZING CHART
F. DEMAND FLOW RATE TOO HIGH F. CHECK SIZING CHART
G. TANK SIZED TOO SMALL G. CHECK SIZING CHART
H. DEMAND FLOW RATE TOO HIGH H. INSTALL MIXING VALVE, ***RAISE TANK TEMP (SEE NOTE BELOW)
I. AIR TRAP IN LOOP I. PURGE TO REMOVE AIR
INSTALL FLOW REGULATOR
I. AIR TRAP IN LOOP I. PURGE TO REMOVE AIR
J. HEAT & TANK COME ON TOGETHER J. RE-CHECK WIRING OR COINCIDENCE
DRAW TANK DOWN AND LOWER HEAT THERMOSTAT. RE-CHECK
K. NOT ENOUGH SPACE HEAT K. BOILER SIZED TOO SMALL, CONSULT CHART
L. SLOW RECOVERY L. CIRCULATOR HEAD CAPACITY TOO LOW

If I had to guess, I'd say the cause for the discharge at my T&P valve was I. AIR TRAP IN LOOP I. PURGE TO REMOVE AIR
INSTALL FLOW REGULATOR. By "Purge" I assume they mean, drain the tank and refill? I need to look at Flow Regulators and Pressure Reducing Valves. Ever since the installation, I've been hearing air in the radiator pipes. This is something we never had before with the old system. And since the installation every winter at some point the boiler will rock and vibrate violently and then stop.

[McG]

You don't think the expansion tank is enough, Red? There is no pressure reducing valve on the water main either after the city meter or after the Superstor cold water inlet shutoff valve.

[Redwood]

By the pressure you state you are right on the borderline of needing a PRV.

You need to figure this system in 2 separate components.

You have the boiler with its expansion tank, PRV, backflow preventer relief valve, and heating loop through the indirect water heater.

You also have the domestic hot water side which is separate, this would include the water supply to the tank which does not pass through the PRV, & backflow preventer for the boiler and the lines to supply the fixtures.

These 2 sides do not intermingle.

If the T&P mounted on the indirect water heater opens it is either a temperature or pressure issue in the water heater that you need to troubleshoot.

If the relief on the boiler is opening one of the causes could be a leaking coil in the indirect water heater allowing DHW at a higher pressure to back feed the boiler which operates typically at a lower pressure. There are also other causes as well.

[jadnashua]

You have two T&P valves, one on the boiler circuits, and one on the WH. They each protect their individual components. As stated, the water between the two do NOT (or at least should not) mix. A typical boiler is a closed system, so it needs an expansion tank. A WH MAY need one, but only if the potable water system is closed (a check valve in the incoming water line, or a PRV). If you do not have a check valve or PRV on the incoming potable water supply, you do NOT need an expansion tank connected to it to account for the WH creating the hot, expanded water.

So, which T&P valve is releasing water?

Your boiler typically has a pressure gauge...what does it read? If you have an auto-fill valve, it could be shot, raising the boiler's water pressure. Or, as Redwood indicated, the WH tank could have a leak between the potable water and the boiler water, which would raise the pressure on the boiler, and cause its T&P valve to release (the SuperStor is a good tank, and unlikely but anything is possible - plus, the pressure relief setting on the boiler is a lot lower than the one on the WH). You probably have a valve before the autofill valve...you could shut that off to see if the water stops flowing.

Air in the WH isn't a problem...as you use hot water, it will be purged. Air in the boiler's circuit to the WH might create problems, and it could prevent any heat from getting to it. If you have hot water, that's unlikely since to get hot, it needs flowing hot water from the boiler, and an air lock could stop that. Any boiler should have an air extraction device. There are various kinds, and some work better than others. Verify what you have, if you have one, is working and not gunked up. I like Spirovents, but there are others. If water isn't flowing through the boiler, it would likely quickly reach its high temperature limit and shut off. It might trip the T&P if there is a lot of mass to the boiler as steam is a lot bigger than liquid water.

Maybe a picture or a diagram of the layout would help. Way back at the beginning, when working properly, it was indicated that a T&P valve can release under any one of two conditions: excessive pressure, or excessive temperature. There is a manual release valve, and if the valve has corrosion or mineral buildups, if it does get opened, it might not close. So, the conditions that caused it to start leaking may have been resolved, but the valve may be bad, and the valve should be replaced.

We're getting some conflicting info, so it's hard to evaluate exactly what is going wrong.

[McG]

If you do not have a check valve or PRV on the incoming potable water supply, you do NOT need an expansion tank connected to it to account for the WH creating the hot, expanded water. I DO NOT HAVE A CHECK VALVE OR PRV ON THE INCOMING POTABLE WATER SUPPLY

So, which T&P valve is releasing water? THE SUPERSTORE T&P. Water Heater.

Your boiler typically has a pressure gauge...what does it read? See picture below

Any boiler should have an air extraction device. See picture below There are various kinds, and some work better than others. Verify what you have, if you have one, is working and not gunked up. I like Spirovents, but there are others.

Maybe a picture or a diagram of the layout would help.

I am slowly beginning to know my way around this system but it is all new to me. The air purge mechanism appears to be missing from the boiler. Unless the "flow control" is for air purging... it is inline with the green boiler expansion tank mounted between the joists.

[McG]

And here is the boiler gauge...

[McG]

...and the "flo control"...which does I don't know what