Boiler Issues! Help!

[MBaker1921]

Hello: New to forum.
I have an older Weil-McClain hot water boiler, single zone, with old style radiators. I noticed some of the radiators were not getting warm so checked water pressure guage. Only about 5lbs of pressure. I added water (Bell and Gossett water reducing valve) and the PRV popped off at only 12 lbs or so. System has a old-style steel expansion tank hung from ceiling. I drained it after turning off the water and power. The PRV weeps so it will need to be replaced for sure. Also, several of the radiators need to be purged of air every few days. System bangs and clangs when boiler fires up.
My question: Since the system is only operating at 5 lbs, why isn't the water reducing valve adding water to the system as it is set to 12 lbs? Is this also in need of being replaced? The expansion tank is not full of water, but could that be part of the problem? Would the best course to keep 10-12 lbs be to replace the PRV and go from there?
Thanks for any help!

 

[Dana]

It's not a pressure/water reducing valve, it's a auto-filler. They are adjustable, and yours may have gone out of adjustment, but that's not the first or only thing I would suspect given the reported systems and brief history.

The screw with locking nut is where the adjustment is made. It's probably less than a half-turn out of adjustment- give it a shot, once you've verified that the gauge isn't lying to you. The hand lever allows you to manually allow more water in (which is what I assumed you did.)

It's also possible (even likely) that your pressure gauge is out of calibration, and needs to be verified with another meter. Most systems will have a drain valve with a hose fitting, and that's a reasonable place to verify the pressure with a separate meter.

At 5 psi most boilers would indeed be making a lot of banging & clanging noises from the flash boil on the heat exchanger plates when the boiler was firing, and it wouldn't be very subtle. You would also likely hear cavitation noises on the system pump(s) at that low pressure. But it should all be pretty quiet at 12 psi, save some gurgling or hiss of air bubbles that have yet to be purged as they pass through the pump.

The PRV is dribbling when the meter is reading 12 psi could be grit in the valve seats. You may be able to purge that by manually opening & closing it a few times. (Careful- there's a serious scald hazard when the system is hot!)

When you drained the system to re-charge the expansion tank you let a lot of air in the system. Unless you did a fair amount of preliminary air-purging it would be normal to still need to bleed the rads fairly often. Most systems will have vents with or without air scoops to auto-purge the remaining bubbles after you've bled the majority.

 

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[MBaker1921]

Yes, I turned down the screwe and it started to fill. It looks exactly like the one you posted. I will change out the PRV valve as it starts to release at close to 10lbs. I hope that will allow the pressure to get up and stay up. Would you recommend replacing the autofill or not necessary? Thanks!

It's not a pressure/water reducing valve, it's a auto-filler. They are adjustable, and yours may have gone out of adjustment, but that's not the first or only thing I would suspect given the reported systems and brief history.

The screw with locking nut is where the adjustment is made. It's probably less than a half-turn out of adjustment- give it a shot, once you've verified that the gauge isn't lying to you. The hand lever allows you to manually allow more water in (which is what I assumed you did.)

It's also possible (even likely) that your pressure gauge is out of calibration, and needs to be verified with another meter. Most systems will have a drain valve with a hose fitting, and that's a reasonable place to verify the pressure with a separate meter.

At 5 psi most boilers would indeed be making a lot of banging & clanging noises from the flash boil on the heat exchanger plates when the boiler was firing, and it wouldn't be very subtle. You would also likely hear cavitation noises on the system pump(s) at that low pressure. But it should all be pretty quiet at 12 psi, save some gurgling or hiss of air bubbles that have yet to be purged as they pass through the pump.

The PRV is dribbling when the meter is reading 12 psi could be grit in the valve seats. You may be able to purge that by manually opening & closing it a few times. (Careful- there's a serious scald hazard when the system is hot!)

When you drained the system to re-charge the expansion tank you let a lot of air in the system. Unless you did a fair amount of preliminary air-purging it would be normal to still need to bleed the rads fairly often. Most systems will have vents with or without air scoops to auto-purge the remaining bubbles after you've bled the majority.

It's not a pressure/water reducing valve, it's a auto-filler. They are adjustable, and yours may have gone out of adjustment, but that's not the first or only thing I would suspect given the reported systems and brief history.

The screw with locking nut is where the adjustment is made. It's probably less than a half-turn out of adjustment- give it a shot, once you've verified that the gauge isn't lying to you. The hand lever allows you to manually allow more water in (which is what I assumed you did.)

It's also possible (even likely) that your pressure gauge is out of calibration, and needs to be verified with another meter. Most systems will have a drain valve with a hose fitting, and that's a reasonable place to verify the pressure with a separate meter.

At 5 psi most boilers would indeed be making a lot of banging & clanging noises from the flash boil on the heat exchanger plates when the boiler was firing, and it wouldn't be very subtle. You would also likely hear cavitation noises on the system pump(s) at that low pressure. But it should all be pretty quiet at 12 psi, save some gurgling or hiss of air bubbles that have yet to be purged as they pass through the pump.

The PRV is dribbling when the meter is reading 12 psi could be grit in the valve seats. You may be able to purge that by manually opening & closing it a few times. (Careful- there's a serious scald hazard when the system is hot!)

When you drained the system to re-charge the expansion tank you let a lot of air in the system. Unless you did a fair amount of preliminary air-purging it would be normal to still need to bleed the rads fairly often. Most systems will have vents with or without air scoops to auto-purge the remaining bubbles after you've bled the majority.

 

[BillTheEngineer]

The water pressure is limited by the safety relief valve. But it is really set by the pressure reducing/auto fill valve.

Usually when theses are messed with in a system that has not been touched in a while they end up needing to be replaced because a little sediment in the plumbing gets in them and messes up the sealing surfaces and they leak. The safety relief valve will drip. The pressure reducing/auto fill valve will leak and the pressure in the system will slowly rise and then the safety relief valve will drip.

When replacing them, make sure you replace the safety relief valve with one that has the proper set pressure (these are factory set and not adjustable and have and ASME stamp on them). The pressure reducing/auto fill valve also needs to be able to work in the appropriate pressure range. Most likely it will need to be adjusted from the factory set point.

 

[Dana]

You can try purging the crud from the PRV by opening & closing in manually (with the little lever on top to see if you can get it to spit the grit and stop dripping by running it a high flow for a second or two. If it still drips at 10 psi after a handful of tries, it's time to replace it.

Unless the auto-fill is bleeding by and overpressuring the system, there is no need to change it out. In fact, auto-fill valves are not really necessary- it's more of convenience, yet often a "solution problem" when the valve seats seep and the system pressure creeps up over days/weeks. You have already discovered what the banging & clanging sounds like when the pressure drops to 5 psi, and that happens WELL before it becomes a safety issue.

 

[MBaker1921]

Yes, I agree with your analysis. There was some question as the if the PRV was adjustable, but clearly it's not. Why it let go at about 10 lbs is a mystery, but maybe just failure due to age.
Thanks!

 

[rjbphd]

Dana, if you look really really close to picture you posted. .label said it's a reducing valve. . That's what it called by the industry standards.