Boiler pressure reducing valve, pressure relief valve or both

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bwana63

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Homeowner, w/zero professional HVAC experience. My 23 yo hot water heating system is discharging water. Not a heavy flow, but steady and significantly more than it used to in previous years (pretty much a trickle).

Figure the pressure reducing valve or pressure relief valve or both are shot. Is one more likely than the other or should I just replace both? Are there other possibilities? I've heard the diaphragms can fail in expansion tanks. But I don't know if expansion tank failure results in excess discharge.

Any quick and dirty way to test these devices, or should I just be thankful that I got 23 years out of them and call it a day? Thanks in advance.
 

Reach4

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I am going to presume that you are talking about water coming out of the T+P (temperature and pressure) valve.

The problem could be that your pressure tank has gone bad. However in that case the flow would not be steady, but it would occur when the heat was on or shortly after. To test for that, you can turn off the water. Open a hot water tap, and let the water run. Then measure the pre-charge pressure at the pressure tank. It should normally be whatever the pressure regulator is set to. If the pressure is gone, or water comes out, the pressure tank is defective. I guess the problem could even be a bad pressure regulating valve and the water into the PFV is over 160 PSI, but that is less probable.

If it is a gas heater, it is easy to tell when the flame is heating.
 

bwana63

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The water is coming from the discharge pipe directly past the pressure relief valve.

I'm clueless about the T+P valve. This heating system is strictly for heat. Have a separate gas water heater. Independent systems. Sorry about my poor nomenclature and these noob questions.

Is the pressure regulating valve the same thing I'm calling the pressure relief valve?

Is the pressure tank the expansion tank?
 

Terry

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I don't know which boiler you have, but after 23 years I'm not surprised that the T&P would be leaking.
Can you post a picture of what you have?
 

Tom Sawyer

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I suspect the expansion tank first although the relief valve may not close now either but the root of the problem is most likely the tank.
 

bwana63

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OK, more info & pics. House (2 story, ~2000 sq. ft above grade) built in 1929, original galvanized piping still in use. Was told (by a heating contractor) that the system was originally steam and subsequently converted to hot water. My system was installed in 93?. Very simple, old school system. One zone. Standard vented boiler. Mine's a Burnham. It's been rock solid. Just clean it before every heating season, turn everything on and forget it.

My gas valve failed and my guy replaced the Honeywell valve that came with the install with a White-Rodgers valve. Seamless transition. My thermocouple has been replaced a couple of times too. External components: B&G pressure reducing valve, air remover, pressure relief valve, Vent-Rite VR60F expansion tank and B&G circulating pump. Could it be any simpler?

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No devices are leaking (the diagnosis would be pretty obvious). The discharge is from the discharge pipe (output of the pressure relief valve). After reading up on expansion tank failures, am thinking mine might be shot.

Also, I should've initially stated that the discharge flow is stronger when the boiler is operating. When the boiler is idle, the flow is definitely less, but more than a trickle. So, there's pretty much always some water being discharged from the system. It didn't used to be that way.

On a side note, do I have a T+P valve? Where is it?
 
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Dana

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The "T & P" stands for "temperature & pressure", and are required on hot water heaters. Hydronic boilers typically have a pressure relief valve or "PRV", that is temperature-insensitive, only opens up when the pressure exceeds it's threshold.

The PRVs shipped with most boilers are set to open up at 30psi. These are not precision instruments, but it'll usually be within a pound or two of that.

That looks like a Burhham P205 or P206? On a '90s vintage P- series there is a pressure & temperature gauge inside the front panel that you remove to gain access to the burners & controls. For a 2 story house with the boiler in the basement the system should be running about 12psi unless you have an unusually tall house. The expansion tank needs to be pre-charged with air to the same pressure that you are running the system. If the the pressure is over 12psi when the system is cold or lukewarm the system pressure is too high.

On a converted steam system there is a lot of water volume, which means the amount of expansion volume difference from when it's hot to when it's cold is substantially higher than on a low water volume system such as baseboards. (The radiator volumes and pipe diameters are considerably bigger.) This means that the expansion tanks will need to be bigger too, and it's possible that yours is sized at the margins. If the system is about 12psi when cold, the pressure will rise a bit as the water warms up and expands, but most of the expansion should be tanken up by the expansion tanke. When fully hot and running it should never go over 25psi unless the expansion tank is undersized or incorrectly charged, or the system pressure was initially set too high.

Often when a PRV opens up once it catches some grit from the heating system water and doesen't fully seat, which could cause it to continuously dribble, but if the system hits the ~30psi even every-other burn cycle you'll be getting constant re-wetting.

Auto-fill valves can fail and over-pressurize the system too, which could be another thing to check out.

A Burhham P-series is nearing end of useful service life at age 23. The heat exchanger plates are usually sufficiently corroded (on both the fire side & water side)at that age to affect combustion efficiency. On it's very best day it's steady-state efficiency was about 80%, and by age 23 it's not unusual to be running at 75% or less. Even though the thing may continue to run another 20 years with occasional repairs, it's not necessarily the "right" thing to do. It's time to at least start thinking about the replacement system, unless you're planning to sell in the next few years. For a typical 2000' house in IL built in the 1920s a P205 is WAY oversized for the actual heat loads, and a P206 is even more so.

With a ZIP code (for weather data) if you can track fuel use against the base-65 heating degree-days between meter reading dates at a nearby weatherstation on degreedays.net it's possible to use the boiler itself as the measuring instrument (however crude) for determining the true heat load at any arbitrary temperature. If you're covered for the 99th percentile temperature bin, that's a very reasonable outside design temperature. Even though it gets colder than that 1% of the time, you're usually still in bed when it does, and you don't really lose much ground temperature-wise indoors until it's been way below the 99% outside design temp for many hours.

I suspect without an insulated foundation but with storm windows & some attic & wall insulation your actual heat load is between 40-50,000 BTU/hr, but in a tightened up better insulated 1920s house with foundation insulation it could be 30K. The P205 puts out 100,000 BTU/hr even when it has degraded to 75% steady state efficiency, and by being 2-3x oversized it's as-used AFUE is nowhere near it's nameplate number. Even the P204 delivers over 70K, even when it's old & decrepit. If you "right size" the replacement boiler it'll hit it's efficiency numbers, deliver longer more efficient burns, which will end up being more comfortable in the end.

Unless the boiler itself is leaking between the heat exchanger plates the replacement plan doesn't have to happen right away. Replacing a PRV is a sub-$50 repair as a DIY, an expansion tank is also in that order of magnitude. But if you have at least the sizing part nailed down in advance, you can then end up optimizing the system down the road when you pull the trigger on a replacement. Most heating & plumbing contractors will be inclined to just replace it with something of similar output, but 9 times out of 10 that's only making their life easy, since they know it'll keep the place warm, but it's not doing YOU any cost, comfort, or efficiency favors.

If you want to run a fuel-use based heat load calc I can explain in more detail how that works. (Or you can probably find threads on this site where I've explained it before.)
 

bwana63

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Wow. Massive and massively helpful. Thank you.

I need time to digest all this. I think I have a P205. I told my contractor to bump up 1 model, since we planned an addition (that never occurred, FWIW). The foundation is uninsulated, the storms are great and the insulation is better than it was (especially in the attic), but with double masonry walls, is not good.

The expansion tank that the current one replaced was huge. Probably 3 times the capacity, mounted between 2 joists. I was shocked by how small the new expansion tank was. But I really knew nothing back then, lol.

The boiler is not leaking. Definitely need to start looking into a new one, although I'll probably roll with the old beast for a few more years. It may make sense to replace my piping too, at least on the first floor. The pipes are fully exposed in the basement (and, yeah, some of them (the main trunks) are rather large and they hang low).
 

Dana

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A fuel-use calc should tell you what you really need for the house where-is-as-is, but it's possible to continue upgrading the thermal performance of the building envelope.

If nothing else, blower-door testing and fixing all of the major air leaks can do quite a bit. The economics of insulating the foundation can be too, if the basement doesn't have to be gutted & re-finished to do it. Further down the list, replacing clear-glass storm windows with low-E storms makes the windows net-energy gainers (even on the north side), and improves comfort, for a lot less money than new code-min replacement windows.

Replacing the fat distribution plumbing won't be cheap, and it won't improve system performance nearly as much as simply right-sizing the boiler to the load. Putting the pipe-replacement money toward air sealing & insulating the foundation walls would make the distribution losses accrue to the house, resulting in warmer floor temps on the rooms above, supporting the heat load.

An addition (even a pretty big one) built to code or better on R-value/U-factor has an astonishingly small effect on the heat load of a house. If the addition is off one end of the house, the heat load may even go DOWN, since instead of a 8" thick double-wythe solid brick wall with a U-factor of ~U0.5 BTU/hr per square foot per degree F, the new walls would have a U-factor of about 0.07. It would literally take 7 x more wall area of new-wall to equal the heat loss of the old brick wall that became a partition wall to the new addition.

It's possible to insulate over masonry walls from the exterior with rigid foam or rigid rock wool, but that's a whole 'nother project to contemplate, with a much bigger budget than a boiler swap or insulating a basement. But on a comfort basis the "payback" of a foam-over can be pretty good, (if not financially with natural gas running at historically low prices.) To hit current code-min for northern IL (US climate zone 5A) with a foam-over takes about 3" of continuous rigid EPS foam or rigid rock wool on the exterior. In southern IL it would only take 2". But there are a lot of details to get right, and the average home improvement or insulation contractor will have zero experience with that type of retrofit. (Most won't necessarily have what it takes even do a basement insulation project right, but check back here if you're contemplating that project.)
 

bwana63

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The house is pretty tight, no leaks that I'm aware of. I'm sure there are some, but I'm a stickler for sealing gaps. Very good storms upstairs, low E, and totally agree that good storms beat average, if not above average, replacement windows, for considerably less. About 500 sq ft of basement is furnished rec room. Wood plank (no panels) walls, thin, inadequate insulation behind them. A lot of work to re-do, including electric. Unfinished basement is more feasible, but still a lot of work. Walls are thin board (Masonite like stuff) over furring strips. Not going to consider going over the brick, for purely aesthetic reasons. Rather live with cold walls.

Sounds like the heating pipes do not need to be replaced (unless they fail). I've had 1 pipe (to a radiator) go in ~23 years.

The 2nd floor definitely is markedly warmer than the first. The first floor is my problem area with heat. It's not bad, but it's noticeably colder than the basement (exposed runs) and 2nd floor. I've thought of installing thermostatic valves (Danfoss) on the upstairs radiators.
 

Dana

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Insulating the foundation with batts-only has a mold & rot risk. In northern IL it's best to put at least R4 as rigid foam (1" EPS or 3/4" of foil faced polyiso) trapped tight to the foundation with an UNFACED batt-insulated studwall. The foam limits ground moisture migration rates into the studwall cavites, while keeping the stud edges above the dew point of the wintertime interior air. Making it 1.5" EPS or 1" polyiso is even better, since it reduces the number of condensing hours at foam/fiber interface at the above-grade section even more (though any liquid moisture would re-evaporate by the time it dribbled down to the warmer zone below grade even with R4.) An inch of EPS (but not polyiso) under the bottom plate of the studwall serves as a capillary & thermal break to keep the bottom plate dry too.

It's best if the studwall has an interior air-barrer (wallboard does it!), with a semi vapor-permeable finish, such as standard latex paint, so the that the stud cavities can dry toward the interior at a reasonable rate.

Seal the seams of EPS with housewrap tape, then seal the tape to the foam with 1/8" of duct mastic troweled or painted on. (No tapes really grab EPS well enough for the long term on their own.) Foil faced polyiso can be sealed with 2" FSK tape (purpose made aluminum duct tape.)

In southern IL you can get away with half that much foam without condensation issues, but use polyiso, or EPS with a facer, since thin EPS isn't sufficiently vapor retardent to limit ground moisture. Come to think of it, 1"-1.5" vinyl or aluminum faced EPS would work fine in northern IL too, since the facers would stick pretty well to housewrap tape.
 

bwana63

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OK, back from Indy and need to get back on track.

Expansion tank replacement: seems pretty simple, am assuming a non-pro can handle it. Shut the system off, close the ball joint water valves, pressurize new tank to 12 psi, put pipe dope on threads, remove old tank (be careful not to get scalded), install new tank. Anything I should be looking out for?

Pressure relief valve: should I buy one of these at the same time as the tank or just the tank and see if that fixes my constant discharge situation? Haven't quite figured out how to take this thing off. Threaded on each end. Think I need to loosen the sweat connection at the PRV output (sweat to female thread copper connector). Then disconnect PRV, and install new PRV in reverse order. Is this right?

Also, any recs on expansion tanks and PRVs?
 

Tom Sawyer

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I would do the relief valve also. There is no T&P valve, only pressure and it's a 30lb relief. Either a Watts 374 or 174 is what you're looking for. Make sure you relieve the boiler pressure before you unscrew anything.
 

bwana63

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I would do the relief valve also. There is no T&P valve, only pressure and it's a 30lb relief. Either a Watts 374 or 174 is what you're looking for. Make sure you relieve the boiler pressure before you unscrew anything.

Thanks for the info. Gonna do both.

Pardon the ignorance, but does one relieve the pressure via the relief valve? (yes, I'm actually asking this question and, yes, I know it sounds incredibly dumb). How does one know when enough pressure has been relieved? (the only thing I know about the PRV (beyond what it does) is that by pressing the lever, water is released and, presumably, pressure is reduced. How much is enough?
 

Tom Sawyer

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Shut the supply off, put a buckt under the relief valve and trip the lever. When it's not spraying out hard, the pressure is off.
 
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