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Heating & Air Conditioning

PRV on boiler still dripping

15 years ago

we have an older weil-mcclain boiler set at 180 and 12# pressure with a 4 year old t-30 amitrol exp tank. replaced a dripping PRV a year ago with an B&G/ ITT 30 psi valve that still drips. i have tripped it many times thinking there might be a slug of crud on the washer. can these valves sometimes be faulty? any thoughts as to how i can correct this? i don't mind buying another valve if will fix the problem this time. thanx in advance for your reply.

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Comments (6)

tk03
15 years ago
What is the cold pressure and the hot pressure on the boiler?
baymee
15 years ago
Is it a steam boiler? That would use a low pressure valve, definitely not a 30#. Otherwise, a 13# valve is too low for a hot water system. You either have a bad valve, a pinhole leak in the domestic water coil, if you have one, too much pressure on the water make-up valve or a bladder leak through the expansion tank.

If the former, changing valves should fix the problem.
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Yes, the zones for lawns and planters are separate. Indeed, our irrigation line taps in before the pressure regulator to the house. At that point the irrigation line is 90-100 PSI and the house regulator set to 60 PSI or so. The irrigation main runs about 50 feet to the first set of automatic valves, then another 50 feet to the next set, and then 30 feet to the last set. So there's some pressure dropoff by the time you reach the backyard. One of the planter zones in the backyard has a total of 18 fixed risers or pop-up sprinklers. I've already tried an outlet like the one pictured above and it works fine. No drip hoses popping off. I'd guess the pressure coming from each drip hose is in the 15-20 PSI range. I found out over the weekend that Rainbird makes pop-up sprinkler conversion kits. Inside the housing is a filter and 30 PSI regulator. Great idea in theory, but having this above ground is just begging to be broken off. I shudder to think of that possibility, especially if nobody notices the damage right away. The flooding would be out of this world. I guess this forces me to use valve boxes all over the yard?
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The pressure won't destroy the boiler if the pressure relief valve works, but it adds fresh water to the boiler which will kill it from rust. So, you want to stop that. It sounds like you have a ceiling hung expansion tank, or multiples. In many cases, opening the drain valve of the tank will not drain it. It becomes vacuum locked because there is only one exit. In stubborn cases, a small hose is inserted through the valve or hole and up to the top of the tank to break the vacuum. The water in the tank must be cold and it makes a mess. The tank must be completely emptied. If it's a continuing problem, I would install an Extrol tank, sized properly. Many times a ceiling hung tank will never give trouble. You don't seem to have a fill valve problem or a pinhole in your domestic coil, if you have one. Since it responds to the heat/cool cycle, I would completely drain the expansion tank or replace with Extrol(s).
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You don't have a PRV (pressure relief valve). You have a TPV (temperature pressure valve), which, unlike a PRV, opens if the temperature or pressure is too high. Since you have replaced the TPV twice without change, it stands to reason that your water temperature or pressure is at least a bit too high. Investigate both. BTW, if you have a PRV on your house water line, you need an expansion tank on the hot water line after the water heater. If you have one, it may have gone bad.
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Comments (5)
Not as familiar with this setup. What I feel confident about is that you haven't had two defective PRV valves. With old valves, you sometimes do get crud between the seat and the washer when you open it that allows it to continue to leak a little. Usually popping it a couple of times flushes it out and solves the problem. But if you were getting dripping before and you have it again now, I would strongly suspect that you are near the point of the valve opening because of temp or pressure. The answer is to actually measure these things and not guess. You need a recording pressure gauge (that shows peak pressure) I've seen these reasonably priced at Lowes and Home Depot. Do this first since the problem is usually pressure related. If that doesn't show up what you expect, then you need to get a recording of the peak temps. That will be a little harder to do, but you need to do it. My Fluke mult-meter will record temp and Min-Max readings. Perhaps you could borrow one.
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sunroomguy
Original Author
15 years ago
It is a water not steam boiler. it does not have a domestic coil. i may have found the problem- pressure in tank is only 5. will increase to 12# and monitor the hot and cold pressure. thank. you.
baymee
15 years ago
I don't hold out much hope of raising the pressure in the tank and stopping the drip.
sunroomguy
Original Author
15 years ago
I've been monitoring the PSI over the weekend. the expansion tank has 11 psi. cold h2o is 11 psi. the burner fires to 180 and 3 different times the psi was 16 to 18. fires back up when down to 140. this morning when it cut out at 180 the pressure went up to 30# and the prv was spurting. i turned down the stat stopping the circulating pump and 10 minutes later the temp was still 180 but the psi was back down to 11. the supply reducing valve is 2 or 3 years old. can anyone help me understand what is happening?
baymee
15 years ago
The boiler must be reduced to zero psi before measuring at the extrol tank. It should read somewhere around 12 pse then. When the boiler aquastat reaches high limit, perhaps 180 in your case, the burner will shut down and the circulator will continue to run as long as there is a call for heat. It will run until is drops to 165-170 and then the burner will start up again if there is still a call for heat. If not, it will sit there until it reaches the low limit or there is a call for heat. It's not unusual for the pressure to increase with the increase in boiler temperature, but if it goes up to 30#, I suspect a BAD extrol tank or one that is not at the right internal pressure.

If your extrol tank has zero pressure when the boiler is at zero, and you charge it to 12# and it doesn't hold for any length of time, then you've found the problem.

I read recently where a system with antifreeze in it can drastically shorten the life of the tank's bladder. Do you use antifreeze?

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