Water dripping out of boiler valve

[Dana]

Find the auto-fill valve (sometimes called a pressure reducing valve. It looks something like this:

On the top stem there is an adjustment screw and a flip-lever for over-riding the pressure control setting to fill the system quickly. There is also going to be a ball valve (3-4" long lever handle) or a gate valve (like the yellow handled valve in the above picture) to isolate the potable water supply.

Turn off the isolating valve, then put a bucket under the outlet down tube of your boiler's pressure relief valve (your top picture), and flip up the lever on the pressure reducing valve to run water into the bucket. Keep an eye on the pressure gauge, and stop the flow when the pressure reaches ~12psi.

Then loosen the locking hex nut on the stem of the auto-fill valve so that it can be adjusted, and crack open the isolating valve between the potable plumbing & auto-fill valve slightly. If you hear water flowing, adjust the screw on the auto-fill until it stops. Check the system pressure- if it's still 12-15 psi you're good to go- open the isolating valve all the way, and you shouldn't hear any more flow. If it's over 15psi you may have to close the isolating valve and bleed off some water to lower the pressure and repeat the pressure adjustment until you get it in the range. (Don't set it very much lower than 12 psi or you may begin to hear flash-boil knocking every time the thing fires up.) With the pressure adjusted, cinch down the lock nut a bit so that the pressure adjustment doesn't change over time.

Keep an eye on the system pressure for a few days/weeks. If the seat to the auto fill valve is worn or has a bit of trapped grit in it there may be water seeping by, slowly overfilling the heating system. If that's the case the auto-fill valve should then be replaced, but if the isolating valve seals well you can get by with it for a long time by just keeping the isloating valve closed.

 

[GG_Mass]

The pressure reducing valve is just behind the heat exchanger next to the drain valve (I can only see part of it in the picture). It has a blue or grey top. Unscrew the bolt on the top of the PRV almost all the way out. Then open the ball valve to start filling the system, after 15 min check the pressure gauge, if it's not at same pressure as the exp. tank (12 psi). Turn the bolt in a bit and wait a few minutes. repeat this until the pressure is where you want it.

So it's possible for the screw on the PRV to stay backed off more than it is now, correct ?

I'm starting the refill with the screw backed off almost on the way, and keep tightening it just until the pressure in the boiler reached 12 PSI, correct ?

 

[Sponsor]

 

[Dana]

That's basically it. When the system reaches 12 psi the sound of water flow through the valve should stop (or be barely audible and waning.)

The temperature & pressure gauge on the boiler isn't exactly a precision instrument and may be miscalibrated. If it's reading a bit higher than reality (= real pressure a bit lower than indicated) the boiler may make some bangs & clangs when boiler is first firing up (or constantly, if the pressure is quite a bit low). Listen to it for the first full burn cycle (or the first clanging & banging sounds that occur- it's not subtle.) If it's giving you the flash-boil bang complaint, the solution is to bump up the pressure a bit at a time until the banging symptom no longer occurs.

 

[GG_Mass]

Drained the boiler down to 0 PSI.

Followed your instructions - loosened the PRV, then introduced water back in, then slightly tightened the PSV until the needle on the tank's gauge rested at ~12 PSI.

Ran the boiler a full cycle - it did not leak this time. (Good news).

The pressure did rise to 25PSI while working, so - I'm just letting the system rest, to make sure the pressure will fall again.


One remark - when I brought the boiler to 0 PSI, the pressure in the expansion tank was also 0 PSI, IIRC, the pressure in the tank should have been 12 PSi, so maybe there is something wrong. I used a crappy gauge this time (the good one's at work), but the crappy one did pick 16PSI in the exp' tank once the system was in full working mode.

 

[Dana]

The tank needs to be pumped up with air to 12 psi as a pre-charge BEFORE pressurizing the system for it to perform it's function. Properly pre-charged the system pressure should stay under 20 psi throughout the burn.

 

[GG_Mass]

Then it seems my exp' tank is not doing its job.

The pressure in it was 0 or close it, when the boiler was at 0 PSI.

I'll bring the quality pressure gauge from work tomorrow, and repeat this process, only this time I'll pump 12PSI of air into the tank - before introducing water back into the system.

 

[Reach4]

I'll bring the quality pressure gauge from work tomorrow, and repeat this process, only this time I'll pump 12PSI of air into the tank - before introducing water back into the system.

Pump air in now, with zero water pressure. Don't worry whether that is 10 PSI or 14 PSI of air at this point. If the air pressure falls, bring a new thermal expansion tank home tomorrow, in addition to your quality pressure gauge for the actual set-up.

Congratulations on finding the problem now instead of when the weather gets cold.

 

[GG_Mass]

Pump air in now, with zero water pressure. Don't worry whether that is 10 PSI or 14 PSI of air at this point. If the air pressure falls, bring a new thermal expansion tank home tomorrow, in addition to your quality pressure gauge for the actual set-up.

Congratulations on finding the problem now instead of when the weather gets cold.

Is there any point in the work cycle, in which the pressure in the exp' tank fluctuates, or it should stay ~12PSi at all times ?

BTW, tonight it's the upper 60's, Thursday night, it should drop to upper 30's at night... so yeah, I'm right on the cusp of it.

 

[Dana]

When the expansion tank is properly charged, as the system pressure goes over the 12 psi pre-charge, the air pressure measured at the tank will track the system pressure. But the pressure swings won't be a lot. (How much the pressure changes with temperature depends on the size of the tank and the total water volume in the system.)

 

[Reach4]

Is there any point in the work cycle, in which the pressure in the exp' tank fluctuates, or it should stay ~12PSi at all times ?

While the water heats, water expands. As that happens, the pressure in the tank will go up. It will match the water pressure.

With a failed expansion tank, the pressure rises enough to drip out of the pressure release. If the tank is too small, the pressure will rise close to the pressure release pressure. There should be enough capacity to keep that from happening.

When the water cools back down, the pressure should drop back to that 12 psi (presuming the refill is set to that). If the fill valve leaks, the pressure will not come back to 12. You can close off the water supply to work around that.

 

[GG_Mass]

Okay -
Decreased the pressure in the boiler to 0 PSI, and with water feed valves closed, pumped the tank to 12PSI, to my suprise, just before opening the valves to let water in and pressurize the tank to 12PSI, I had a look at the tank's gauge, and it was back to 19PSI, not sure how.

While I was pumping air into the exp' tank, the pressure in the boiler went up, without letting water in.

Any ideas ? (is this a certainty now that the exp' tank is bad ?)

Thank you.

 

[Reach4]

(is this a certainty now that the exp' tank is bad ?)

I was going to just say yes, but I am not totally certain.

Your air gauge said 12, and the pressure gauge on the system said 19 at the same time? I think at least one of your gauges is wrong.

I still think you very probably have a bad pressure tank. You can be sure when you open the water drain while adding air to the pressure tank. That might have the negative consequence of adding air to your water. So get the gauge problem figured out, or, even better, replace the tank with the remote chance that it is good.

 

[Dana]

Uhhh... NO!

When the bladder in a tank fails the whole tank fills up with water, and water dribbles out of the air-filler valve when pressed. Try bleeding a bit of air out- if it pees all over you the tank is bad. If it's just hissing rather than pissing it's fine. If it happens that the air valve is leaky it can lose it's pre-charge over several days, which would an issue, but it's pretty easy to check for air leaks at the valve with hand or dishwashing liquid & water.

With the system's isolation valve closed or the autofill pressure adjustment dialed down, and the system pressure has been bled down by releasing some water, pumping air into the expansion tank SHOULD make the system pressure go up. By pumping air into the tank it pushes water out the other side of the tank back into the system causing the system's pressure to rise. But the system pressure shouldn't be (can't be, in reality) higher than the air pressure in the tank.

The fact that the system pressure gauge was reading 19 psi when you had only pumped the tank to 12 psi is an indication that the boiler's GAUGE is bad, or your air pressure gauge is bad. One gauge or the other or both are probably just miscalibrated- they're not precision instruments, but a 7 psi difference is quite a bit. There may be something else going on- maybe the gauge sticks a bit, who knows. But you can still get there from here.

Try bleeding off a bit more water from the system, and see if the pre-charged air pressure changes- it shouldn't by very much, but if it drops, keep adding air until the air pressures reads ~12 psi even when the system pressure gauge is reading << 10 psi. Then, adjust the auto-fill valve to where it just begins to add water to the system, then see what the system pressure gauge reads. If the boiler's gauge still reads < 10 psi, tweak the auto-fill adjustment until it's at 12 psi, then check the air pressure again. If the gauges are reasonably well calibrated the air pressure should still be ~12 psi.

 

[Dana]

Needless to say (but I'll state it anyway), it's a lot easier to set the pre-charge pressure before it's plumbed into the system, since when it has the uncompressible water on the other side any time you add air into the tank, more water has to be bled off the system, or you'll just be pressurizing a very small air volume, not the expanding the bladder to anywhere near the full volume of the tank. When going about it in this piecemeal manner it's necessary to keep bleeding water as you add air, to ensure that the system side's pressure is well below that of the expansion tank, and the expansion tank is fully pre-charged before you bring the system up to pressure with the auto-fill.

 

[GG_Mass]

I understand.

I'm going to assume, for now, that the tank's gauge is off by 5PSI. The digital automotive gauge I use is pretty good, very good, actually. Its MOE is +/- 0.5PSI, and it's been tested against TPMS sensors quite a few times and was always trustworthy.
The boiler is more than 30 Years old and has a needle type gauge.

I'll do this for now - I've started the system, the good thing is, that it's not climbing to the 25-30 PSI area anymore, but stays around 20PSI, +/- 5 PSI places it around 15PSI (if going by the (-) ), which is where the tank is at, when the system is running.

So far, I've only tested one heat cycle at a time, yesterday, then today, in which there were no lakes. I will keep the system on and watch it through multiple cycles, and see if leaks occur.

 

[Dana]

Sounds like you have enough air in the tank and it's at a reasonable operational pressure (though a bit lower would still be fine), so it should run just fine for years, as long as...

A: ...the auto-fill valve isn't seeping, overfilling the system and...

B: ...there are no air leaks on the tank.

Both failure types are pretty common, but the risk of either in any given calendar year is in low single-digit percentages. Most systems will go a couple or three decades without experiencing either. When it's time to replace the boiler it's customary to swap them out. The bladders in the tanks can get brittle with age, and after 25 years the risk starts to go up. Grit can find it's way into the auto-fill valve seat pretty much any time, but usually doesn't- some are working fine after 5 decades of service.

For the perennially vigilant or obsessive worriers it's worth checking and adjusting the pre-charge level every 2-3 years even if there aren't any symptoms. (That said, I haven't tested the charge level on my tank in more than 5 years, and I'm still worried. The system pressure gauge gets eyeballed at least 3-5 times/year, and as long as it's fine, I'm fine. YMMV.)

 

[GG_Mass]

I may be dealing with a sipping auto fill valve (it was also called a pressure relief valve in this thread), it's the valve with a thumb screw in it, which regulates the water pressure allowed into the boiler).

The boiler cycled a few times now, there were no leaks, but the resting pressure in the tank seems to pass the 20PSI again, close to 24PSI I'd say.

You've mentioned grit may find itself into the valve - the town water lines are having massive work done on them, and when that happens, we usually get pretty dirty water, and it's been going on for two weeks now.

That valve, I'd say - is much (10, maybe more years) older than the exp' tank, may as well be the original. The exp' tank is not 40 years old and is probably a retrofit.

 

[Dana]

Auto-fill is also known as a pressure REDUCING valve. The pressure RELIEF valve is the one on the boiler that spits water every burn cycle when the system pressure goes too high. People often use "PRV" to refer to either, which makes it confusing, which is why I tend to use the term "auto-fill" rather than pressure-reducing valve in this context, and usually type out "pressure relief valve" rather than a 3-letter monicker.

If there is ball valve between the auto-fill and the potable supply, turn it off and bleed some water to bring the system pressure back down to a reasonable range. The auto-fill is there primarily as a convenience to the person installing and maintaining the system rather than a safety factor, and isn't really necessary. With the water supply to the auto-fill shutoff there is no way for water to get into the system unless your plate-type heat exchanger to the water heater is developing a pinhole leak. (It happens.) If the isolating valve to the auto-fill is a gate valve rather than a ball valve it too could seep water- they're not nearly as reliable as a ball valves. But whatever the type, give it a shot. If it stops the slow pressure gain it points toward the auto-fill being the culprit.

 

[Jadnashua]

When working correctly, once your boiler system is filled with water, it should never need any more again until you must service something! An autofill valve can mask a slow leak, and keep the system at design pressure so it won't shut down from too low of a pressure, but other than that, they can be more of a nuisance than a benefit when or if they start to leak and bleed pressure into the system that is not needed or wanted.