# 30 lb T&P Relieving at 33 psi, Even at 175 Degrees



## etbrown4 (Dec 25, 2011)

Looks like 30 lb. T&P is performing as it should.

Seems odd for this residential boiler to be running much above 25psi at these temps.

Aquastat is pretty much ruled out as we just have too much pressure at this temp.

Tips appreciated.

Possibilities include the flue which appears clear, internal unit cleaning which has been done (not certain how well), and I guess there is always the chance the circ pump is delivering lower than spec'd gpm. It circulates seemingly well enough, but just have too much pressure for the temp.


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## AWWGH (May 2, 2011)

etbrown4 said:


> Looks like 30 lb. T&P is performing as it should. Seems odd for this residential boiler to be running much above 25psi at these temps. Aquastat is pretty much ruled out as we just have too much pressure at this temp. Tips appreciated. Possibilities include the flue which appears clear, internal unit cleaning which has been done (not certain how well), and I guess there is always the chance the circ pump is delivering lower than spec'd gpm. It circulates seemingly well enough, but just have too much pressure for the temp.


Did you check the expansion tank???


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## etbrown4 (Dec 25, 2011)

not yet!

It's a 65 year old tank hung on the wall.

Did these have rubber bladders back then?


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## plumbingdept (Mar 19, 2015)

i ran into this also, so annoying. changed everything twice the fast fill, the expansion tank the releif valve, and the aquastat. the circ was fine. anyway we ended up just setting the pressure at 12 psi then turning off the water supply ball valve and that fixed it. water pressure in the house was 75 psi which is not abnormal for my area. never really found out the source of the problem. the boiler did run fine the 10+ years before problem happened


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## AWWGH (May 2, 2011)

etbrown4 said:


> not yet! It's a 65 year old tank hung on the wall. Did these have rubber bladders back then?


 No, but it also probably has no air charge. No room for expansion then you're gonna pop the relief valve.


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## AWWGH (May 2, 2011)

plumbingdept said:


> i ran into this also, so annoying. changed everything twice the fast fill, the expansion tank the releif valve, and the aquastat. the circ was fine. anyway we ended up just setting the pressure at 12 psi then turning off the water supply ball valve and that fixed it. water pressure in the house was 75 psi which is not abnormal for my area. never really found out the source of the problem. the boiler did run fine the 10+ years before problem happened


Did you try plugging the relief valve?


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## plumbdrum (Nov 30, 2013)

AWWGH said:


> Did you try plugging the relief valve?


That's the best advise yet.


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## etbrown4 (Dec 25, 2011)

I won't be plugging the releif valve.

Would prefer to find and fix..

So for an oldie tank it's just 10-12 pis of air first and refill?

.........................................................

To the poster who said he shut off his water supply.......that sounds like an exceptionally bad idea as boilers consume water over time...that why the auto water feeder is there. You are risking an over pressure situation, and you'd best pray that the relief valve works and does not stick! If an inspector caught this he would red tag your unit for all the right reasons.


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## plumbdrum (Nov 30, 2013)

Mr Brown, you obviously do not have much experience in the heating industry


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## AWWGH (May 2, 2011)

etbrown4 said:


> I won't be plugging the releif valve. Would prefer to find and fix.. So for an oldie tank it's just 10-12 pis of air first and refill? ......................................................... To the poster who said he shut off his water supply.......that sounds like an exceptionally bad idea as boilers consume water over time...that why the auto water feeder is there. You are risking an over pressure situation, and you'd best pray that the relief valve works and does not stick! If an inspector caught this he would red tag your unit for all the right reasons.


Plugging it was a joke. 

For a standard application 12psi charge should be fine.

As for the shutting off the automatic feed, I don't agree with it but I also don't agree with boilers "consuming" water. Once a boiler is filled and all of the air is purged properly of the system it will not use any water. (Obviously talking about water not steam). It's a closed loop system, if your boiler is consuming water then you have a leak.


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## AWWGH (May 2, 2011)

plumbdrum said:


> Mr Brown, you obviously do not have much experience in the heating industry


 He's from NC, I worked with a guy from down south one time and I kid you not this is a quote after he quoted a boiler job with four zones and gave me like 1 tee for the manifold. "You got to take it easy on me, we don't have boilers where I'm from we've got heat pumps! The only place down there that have boilers is on millionaire road!" Accent and all lol


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## plumbdrum (Nov 30, 2013)

etbrown4 said:


> Looks like 30 lb. T&P is performing as it should. Seems odd for this residential boiler to be running much above 25psi at these temps. Aquastat is pretty much ruled out as we just have too much pressure at this temp. Tips appreciated. Possibilities include the flue which appears clear, internal unit cleaning which has been done (not certain how well), and I guess there is always the chance the circ pump is delivering lower than spec'd gpm. It circulates seemingly well enough, but just have too much pressure for the temp.


Ok first off it's a pressure relief valve not a T&P, second you obviously have a pressure problem to which it could be a few different scenarios 
1- expansion tank ( bladder diaphragm blown, or tank type water logged)
2-pressure reducing valve not working properly ( which is why you would shut it off to verify if boiler is building pressure)
3-tankless coil ( if there is one) could have pin hole in the coil building up your pressure.


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## plumbingdept (Mar 19, 2015)

AWWGH said:


> Plugging it was a joke.
> 
> For a standard application 12psi charge should be fine.
> 
> As for the shutting off the automatic feed, I don't agree with it but I also don't agree with boilers "consuming" water. Once a boiler is filled and all of the air is purged properly of the system it will not use any water. (Obviously talking about water not steam). It's a closed loop system, if your boiler is consuming water then you have a leak.


as far as turning off the auto feed it was not an easy decision to make to be honest. that was last year and im still thinking about it. there was no tankless coil or indirect water heater at this job. what really boggles me is that the pressure was set at 12 then when boiler went on it would go over 30 but what kills me is why did it stop happening when i turned off the water supply. how was that the problem if it was fine at stand still and cold. it really should not have affected it but that ended being the problem solver. HO was informed


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## MootsNYC (Dec 19, 2013)

Have you cut the water supply line and see if it passing slightly? And where is the supply line tied into?


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## plumbdrum (Nov 30, 2013)

plumbingdept said:


> as far as turning off the auto feed it was not an easy decision to make to be honest. that was last year and im still thinking about it. there was no tankless coil or indirect water heater at this job. what really boggles me is that the pressure was set at 12 then when boiler went on it would go over 30 but what kills me is why did it stop happening when i turned off the water supply. how was that the problem if it was fine at stand still and cold. it really should not have affected it but that ended being the problem solver. HO was informed



By saying auto feeder I assume you mean a pressure reducing valve with a fast fill. Sometime those valves get scaled up with crud and will trickle water in after your set desired psi (12-15 psi for a standard heating boiler) by setting the pressure and shutting off the incoming water besides a expansion tank problem, how else would it build up pressure. So for the short term to isolate a problem shutting off valve is a quick fix (more for just trouble shooting) replace "auto feed" and make sure there is a proper cross connection device installed and you should be good to go.


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## PLUMBER_BILL (Oct 23, 2009)

*From the past before bladder tanks*



plumbdrum said:


> By saying auto feeder ,>SNIP<
> 
> Remember the fun of draining those old 12 x 30 tanks, when there was not a drain valve installed that allowed you to pull the 1/8" plug to allow air in the
> tank. Trick was to take a 1/8" inch piece of copper about 15" long and with
> ...


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## plumber11928 (Feb 18, 2015)

Back in "78" when i first started working on boilers an old timer that was teaching me made me blow into the hose till the tank emptied out. Talking about learning the hard way. Now i know why he was laughing...lol
Miss you Chuck...RIP


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## etbrown4 (Dec 25, 2011)

This boiler must be partly female.

With the old style expansion tank emptied and just holding ambient air, and the water feeder on, it still runs up to 33 psi at 175, in 3-5 minutes of run time.

Here is the kicker. with the water feeder off, and again with the tank just initially holding ambient air initially, I get 0 psi at startup, and 0 psi at up to 190 degrees.

The boiler pressure with the feeder on, at rest is 12 psi, when cool.

Tips appreciated.


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## plumbdrum (Nov 30, 2013)

My tip would be to call a heating professional


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## etbrown4 (Dec 25, 2011)

Yes, plumbdrum is right , we need more experience with this kind of old timey expansion tank. We've been doing plumbing and heating since the mid 1970's but only install a few boilers each year.

Some guys call this a European style. It's 65 years old and hangs high on the wall. It's about 18" in diameter, and only projects from the wall about 8-9", holding maybe 2 gallons.

Because there are no fittings on this expansion tank, and no label, you can't tell if it has a bladder and if it's pre-charged. It's very different from current tanks, as it's fed with a true 5/16" od copper line, and that's it.

Interested to know if others have worked with this unusual style tank.


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## AWWGH (May 2, 2011)

etbrown4 said:


> Yes, plumbdrum is right , we need more experience with this kind of old timey expansion tank. We've been doing plumbing and heating since the mid 1970's but only install a few boilers each year. Some guys call this a European style. It's 65 years old and hangs high on the wall. It's about 18" in diameter, and only projects from the wall about 8-9", holding maybe 2 gallons. Because there are no fittings on this expansion tank, and no label, you can't tell if it has a bladder and if it's pre-charged. It's very different from current tanks, as it's fed with a true 5/16" od copper line, and that's it. Interested to know if others have worked with this unusual style tank.


It's not unusual, it's just an old expansion tank that they used before they came out with pre charged bladder tanks.

Recharge the tank or cut it out and install a new (properly sized) expansion tank with a bladder. I don't think you understand that the air charge is there as a cushion, as the water heats it expands. If that tank is water logged and has no air charge have no room for expansion you are going to pop the relief valve.


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## etbrown4 (Dec 25, 2011)

Thanks AWWGH. Sure most of the xtrols we've worked with have the 12 psi precharge.

My understanding of the older, non-precharged tanks is they they supposedly rely on ambient air which is there when the tank is open before piping in. If we have it right, that ambient air at 0 psi originally, becomes the cushion of air against which the water pushes - allowing for the expansion. 

Problem is, working with this ambient air, which is there in theory, after draining the tank and restarting, we're still seeing 33 or so psi in heating operation. Each time we go back to drain the tank, it seems to have been full of about 2 gallons of water.


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## rwh (Dec 17, 2014)

Your compression type tank is going into a vacuum when you drain it. Air must be introduced or it will fill with water every time.


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## AWWGH (May 2, 2011)

etbrown4 said:


> Thanks AWWGH. Sure most of the xtrols we've worked with have the 12 psi precharge. My understanding of the older, non-precharged tanks is they they supposedly rely on ambient air which is there when the tank is open before piping in. If we have it right, that ambient air at 0 psi originally, becomes the cushion of air against which the water pushes - allowing for the expansion. Problem is, working with this ambient air, which is there in theory, after draining the tank and restarting, we're still seeing 33 or so psi in heating operation. Each time we go back to drain the tank, it seems to have been full of about 2 gallons of water.


The tank inlet could be plugged essentially eliminating the tank from the system. Being a plumbing professional and knowing the cost of an expansion tank, a tap tee, a few tank supports, and a cap or two I would cut old tank out and install a new tank.


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## plumber11928 (Feb 18, 2015)

Maybe..Just maybe ... If your draining the tank empty then filling the system to normal operating pressure, when you fire up the system to operating temp and the gauge reads over 30 psi and the relief valve is not opening, you may have a fast gauge. Just a thought.


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## AWWGH (May 2, 2011)

When the burnham mpos first came out we got one that was programmed in Celsius rather than Fahrenheit, popped the relief valve on startup and scared the hell out of us. 180 Celsius no Bueno


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## CTs2p2 (Dec 6, 2011)

AWWGH said:


> When the burnham mpos first came out we got one that was programmed in Celsius rather than Fahrenheit, popped the relief valve on startup and scared the hell out of us. 180 Celsius no Bueno


With burnhams history of leakers I'm surprised the relief valve is all that popped!


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## CTs2p2 (Dec 6, 2011)

etbrown4 said:


> Thanks AWWGH. Sure most of the xtrols we've worked with have the 12 psi precharge. My understanding of the older, non-precharged tanks is they they supposedly rely on ambient air which is there when the tank is open before piping in. If we have it right, that ambient air at 0 psi originally, becomes the cushion of air against which the water pushes - allowing for the expansion. Problem is, working with this ambient air, which is there in theory, after draining the tank and restarting, we're still seeing 33 or so psi in heating operation. Each time we go back to drain the tank, it seems to have been full of about 2 gallons of water.



2 gallons of water out of an old style expansion tank isn't draining it.. You aren't even putting a dent in it, it's probably a 20 to 30 gallon tank. Where is the pictures? I'm also picturing Mr. Parrs glop glop glop sound while you're "draining" it 
Change the tank as AWWGH has already stated, probably a new feeder/back flow too if you suspect it's sticking, probably don't want anymore callbacks as it is, cheap insurance


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## Redwood (Sep 8, 2008)

AWWGH said:


> When the burnham mpos first came out we got one that was programmed in Celsius rather than Fahrenheit, popped the relief valve on startup and scared the hell out of us. 180 Celsius no Bueno


Try a 100 psi or so relief...:laughing:
Might be enough off the top of my head...

I didn't know MPO's had a superheater...:laughing:


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## CTs2p2 (Dec 6, 2011)

Redwood said:


> Try a 100 psi or so relief...:laughing: Might be enough off the top of my head... I didn't know MPO's had a superheater...:laughing:


I don't think it made it to 180*C

That's in the neighborhood of 350F haha


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## Redwood (Sep 8, 2008)

CTs2p2 said:


> I don't think it made it to 180*C
> 
> That's in the neighborhood of 350F haha


Yea... Something wrong... :laughing:


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## etbrown4 (Dec 25, 2011)

Problem solved with new expansion tank.Now 180 degrees and 12 psi.

Thanks especially to CTs2p2 and AWWGh as you were right on the money, and to others who offered advice!

That old expansion tank was European style and small, not holding over 2 gallons. Either way, we'll never know if it had a bladder or not, or if it was in vacuum, but I agree it's easier to start over and quit fooling with the old tank.


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## plumbingdept (Mar 19, 2015)

I ended up finding out what was going on. the water feed was tied in on the return and so was the circulator, the expansion tank was on the feed though (yes weird) so when the circ pump kicked on the pressure differencial caused a drop in pressure behind it (where the feed was) so the prv saw it as there was not enough pressure so it added water. then when there was too much pressure after the circ it blew the relief valve. anyway im not sure if im explaining it that well but i found it in a dan holohan book and it made sense


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## plumbdrum (Nov 30, 2013)

Redwood said:


> Yea... Something wrong... :laughing:


Would the real redwood please stand up


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