Replace Pressure Reducing valve and Backflow Preventer Weil Mclain CGA

[Jason1]

Hello all,

I have a Weil Mclain Gold CGa boiler that is about ten years old and the backflow preventer let out some water. The pressure reducing valve has green deposits at the bottom of the brass union nut which has developed a small leak. It's a Bell and Gosett 1/2" pressure reducing valve and Watts 1/2" backflow preventer:
https://www.supplyhouse.com/Watts-0063190-BBFP-1-2-IPS-Backflow-Preventer

The expansion tank seems fine. I tapped on the upper half which sounded full and the lower half which sounded hollow. I removed the cap at the bottom and it was dry, no water leaking out.

So I need to replace the pressure reducing valve and backflow preventer at a minimum. I plan on leaving the expansion tank because it appears to be fine for now.

I have one shutoff valve before the pressure reducing valve and another shutoff valve right after before the water enters the boiler, so I can isolate the pressure reducing valve and backflow preventer by closing the two valves.

To do the repair I need to:

1. shutoff both water valves to isolate the pressure reducing valve and backflow preventer
2. turn off the burner
3. remove the pressure reducing valve and backflow preventer
4. install the new pressure reducing valve and backflow preventer
5. open both shutoff valves closed in step 1. and turn the burner back on.

Am I missing any required steps for this repair?

Do I need to increase the pressure on the pressure reducing valve or leave it at the factory setting of
12 psi? The house is two story.

Is it necessary to drain the boiler and purge air from the zones before turning the boiler back on?
My guess is no because the parts being replaced are isolated from the system by the two shutoff valves.

Thank you in advance.

 

[John Gayewski]

The expansion tank has a schrader valve on it. You need to check it to see if the expansion tank is full. First use a gauge on it to try to record the pressure. Should be around 15 psi. If no water comes out of it and only air comes out then your expansion tank is, as you suspect, likley fine. Your pressure reducing valve should be set just one psi or so higher than your expansion tank. Assuming your in a one or two story house the 12 to 15psi range should be good.

You likley won't introduce enough air to cause a problem, your air vents should be able to expel it unless your talkong about a long stretch of piping. Depending on what type of air expulsion devices you have they may need to be opened for a little while while you circulate the water, after your repair.

Edit flip flop the pressures. Prv should be lower. Half sleep brain.

 

[Sponsor]

 

[Jason1]

Thank you John,

Will any type of bicycle pump work for checking pressure and increasing pressure on an expansion tank. For example:
https://www.target.com/p/franklin-sports-ball-maintenance-kit/-/A-12945154

My boiler has an air eliminator at the top of the expansion tank with a bleeder cap. Like in this picture:
https://www.supplyhouse.com/Amtrol-...4-NPT-Air-Eliminator-Air-Vent-Boiler-Trim-Kit

Should I open the bleeder cap more after I do the repair and circulate the water, or should the setting as is be fine for releasing whatever air enters the system from doing the repair?

Can I check the pressure on the expansion tank while it is on the boiler or do I need to remove the expansion tank and then test the pressure?
After ten years would it have lost pressure and need to be reset to about 12-15 psi?

 

[John Gayewski]

You should be able to isolate the expansion tank so that it may be changed. But you don't need to isolate it to check the pressure. You want it to be above the set point of the prv while in operation so that your prv isn't pushing water into it. Only the expansion of hot water should push water into it. (I belive I said that backwards last night while letting the dog out and half asleep. Sorry about that.

You just want to make sure gravity would have the water on top of the schrader valve so that you would see it come out if the bladder was leaking.

 

[John Gayewski]

Yes open the cap on the air vent until you have good flow everywhere. Yes a bicycle pump will be fine.

 

[Jason1]

Yes, the expansion tank is higher than the prv and can be isolated with its own shutoff valve.

I'm thinking its better to replace the expansion tank because of its age - 10 years. Since I'm already working on the machine, might as well do a complete job. I'll feel like a fool if I replace the prv and backflow preventer and then the expansion tank fails in 6 months.

How long should the system run to bleed the introduced air out if I'm using the bleeder cap on top of the expansion tank?
10 minutes, 1 hour, a few hours?

 

[John Gayewski]

That depends on a lot of things. Mostly how long it takes for air to find the valve.

You should hear air come out. Then a few minutes later a little more. That should be it. It's more about checking your sytem near and around the emitters to make sure your getting flow to them everywhere. If you had good flow and heat everywhere and you lose heat to an emitter somewhere, then you know you have air trapped and needed to go longer. Other than that it shouldn't be more than a few cycles of water around the system.

 

[Sylvan]

The expansion tank has a schrader valve on it. You need to check it to see if the expansion tank is full. First use a gauge on it to try to record the pressure. Should be around 15 psi. If no water comes out of it and only air comes out then your expansion tank is, as you suspect, likley fine. Your pressure reducing valve should be set just one psi or so higher than your expansion tank. Assuming your in a one or two story house the 12 to 15psi range should be good.

You likley won't introduce enough air to cause a problem, your air vents should be able to expel it unless your talkong about a long stretch of piping. Depending on what type of air expulsion devices you have they may need to be opened for a little while while you circulate the water, after your repair.

Edit flip flop the pressures. Prv should be lower. Half sleep brain.

Actually, To properly set the automatic feeder ideally using decent heating practices it is set as follows

1- Fill the system and check your altitude gauge cold fill (tri indicator) then add 4 PSI to allow for a fudge factor

2- So if your cold fill pressure is 20 PSI you take 20 PSI times it by .433 - 8.66 PSI knowing 8.66 PSI will elevate water 20.00 feet (8.66 X 2.31)


The fudge factor is to allow for bleeding the system when required

Normally An expansion tank is sized by the BTU INPUT of the boiler as there is something called pressure temperature relationship

To check the expansion tank it has to be removed from the system to know what the actual pressure it has and same when charging the tank

 

[Jason1]

Thank you all.

For a 2 story home with 4 zones should the pre-charge 12 psi be enough on the pressure reducing valve and the expansion tank to adequately circulate water, or will I have to increase the pressure by 3-4 psi on both the prv and the expansion tank?

To increase the cold pressure on the prv, with the heat off and the water on I adjust the screw on the unit counterclockwise while reading the gauge on the boiler until it reads the desired psi.

To increase the pressure on the expansion tank, I use a bicycle pump on the schrader valve to increase the psi before installation.

Does everything sound right?

 

[John Gayewski]

Actually, To properly set the automatic feeder ideally using decent heating practices it is set as follows

1- Fill the system and check your altitude gauge cold fill (tri indicator) then add 4 PSI to allow for a fudge factor

2- So if your cold fill pressure is 20 PSI you take 20 PSI times it by .433 - 8.66 PSI knowing 8.66 PSI will elevate water 20.00 feet (8.66 X 2.31)


The fudge factor is to allow for bleeding the system when required

Normally An expansion tank is sized by the BTU INPUT of the boiler as there is something called pressure temperature relationship

To check the expansion tank it has to be removed from the system to know what the actual pressure it has and same when charging the tank

The formula for SIZING an expansion tank is delta t x volume (gal) x .00023

The expansion tank has already been sized by the installer. We aren't sizing that. All we are looking for here is fill pressure (getting the water to the top of the system)plus a little to put some squeeze on the entrained air. The circulator will add its differential pressure to the system. No fudge needed. As I said. 12 to 15 psi is considered normal.

There's actually no reason to confuse this and make it convoluted.

 

[John Gayewski]

The 12 psi is not really to aid circulating. You just need enough pressure to fill the system. So the elevation from your fill valve to your highest emitter. Is the consideration. Your circulator doesn't do any lifting. Yes 12 psi should be enough, that'll lift you 27 feet high, so you should be more than OK.

 

[Sylvan]

The formula for SIZING an expansion tank is delta t x volume (gal) x .00023

The expansion tank has already been sized by the installer. We aren't sizing that. All we are looking for here is fill pressure (getting the water to the top of the system)plus a little to put some squeeze on the entrained air. The circulator will add its differential pressure to the system. No fudge needed. As I said. 12 to 15 psi is considered normal.

There's actually new reason to confuse this and make it convoluted.

"The expansion tank has already been sized by the installer"

What makes you think the "installer" had any formal training?

Possibly the installer asked the guy at the service counter what do YOU suggest is the correct size?

Never assume the installers actually know what they are doing

There is no license requirements for heating in NY, unless it is high pressure (15 PSI or above)

 

[Sylvan]

Yes, the expansion tank is higher than the prv and can be isolated with its own shutoff valve.

I'm thinking its better to replace the expansion tank because of its age - 10 years. Since I'm already working on the machine, might as well do a complete job. I'll feel like a fool if I replace the prv and backflow preventer and then the expansion tank fails in 6 months.

How long should the system run to bleed the introduced air out if I'm using the bleeder cap on top of the expansion tank?
10 minutes, 1 hour, a few hours?

Consider buying one of these located at the boiler as it can remove micro bubbles

I install these on every hydronic boiler we install and never had a call back

https://www.supplyhouse.com/Spiroth...MYVkRg0kSJeLndN5WXLtk7VJov-zzUThoCTWcQAvD_BwE

 

[Sylvan]

<<<< educational

 

[Sylvan]

 

[Jason1]

I'll use the same size and model expansion tank from my local plumbing supply store.

I plan on shutting off the
1. valve for water in to the boiler,
2. valve from the boiler to the zones,
and 3. return valve before I remove the existing expansion tank.

Do I need to lower the boiler pressure to zero before removing the expansion tank to avoid taking a shower.

If yes, what's the best way to do that? Open the boiler drain valve a little bit until the tridicator reads zero psi?

My system has an air Eliminator at the highest point above the expansion tank before the water travels to the zones, so do I need to purge the air from the boiler separately by running water through the system with the drain valve open? Or will any air that enters the system during the expansion tank replacement get purged on its own from the air Eliminator at the highest point above the expansion tank?

I have something like this:
https://www.supplyhouse.com/Resideo-PV100S-1-Sweat-Supervent-Air-Eliminator

Thanks.

 

[Jason1]

Also, what psi should the expansion tank be set at. Should it be left at the factory pre-charge of 12 psi or set to the working pressure of the boiler.

For example, when the heat is on the psi is 18. So should the expansion tank be set at 18 psi before installation. Thanks.

Or if you're replacing the prv and expansion tank at the same time, leave both at the factory pre-charge of 12?

 

[Fitter30]

System off and water temp below 100* set ex pressure same as system pressure. If adding air to ex tank use a hand tire pump or be very careful with a air compressor are blow the bladder.

 

[Jason1]

After I replace the prv and expansion tank, to reset the cold pressure in the boiler my understanding is I need to open the boiler drain and the valve feeding water to the boiler while watching the tridicator and then manipulate the auto feed lever on the prv to increase the pressure until it is at the desired 12 psi, and then shut off the boiler drain.

Is this correct? Because I will have a drop in pressure when I remove the expansion tank even with all the valves feeding the system shut off.

I have one of these installed at the highest point with the expansion tank attached to it so I don't see purging air as being an issue in my setup.
https://www.supplyhouse.com/Resideo-PV100S-1-Sweat-Supervent-Air-Eliminator

 

[Sylvan]

Jason, a lot going on there .. Imagine if you had this boiler to service?