Boiler losing pressure

GeneBA

I posted recently in another thread about some plumbing errors. Very thankful for suggestions. Contractor took care of few things. DHW delivery is working. Combi boiler, Navien NCB 190/080 is losing pressure in space heating loop. Zone valves, pump and thermostats are off. System is set up for 12 psi, Navien default. Every morning I’d find psi display at 7.9 psi and boiler goes into lock out. I use auto feed vavle to add water, wait few minutes for Navien to “sense” and good again. This model also has built-in valve to add water. I hear clicking all the time.

Contractor can’t figure this out. We replaced expansion tank with brand new 12 psi. Boiler relief valve looks fine to him. No dripping. Purged air multiple times and he can’t see any leaks. This is a closed loop floor system and space heating is off.

why is pressure dropping.

would appreciate any suggestions

hot_rod

Can you pressurize the system to 12 psi and not run it for a day, even 4 hours? It it started warm, you may see a few psi drop as the water cools.
Does it ever drop to 0 psi? How low has it gone down to?

Can you isolate the expansion tank?

If it drops to 7.9 and never lower, the leak would be above the level of the water at 7.9 psi

yellowdog

is the water going down the condensate drain? and thats why it doesn't show anywhere?

GeneBA

hot_rod said:

Can you pressurize the system to 12 psi and not run it for a day, even 4 hours? It it started warm, you may see a few psi drop as the water cools. Does it ever drop to 0 psi? How low has it gone down to? Can you isolate the expansion tank? If it drops to 7.9 and never lower, the leak would be above the level of the water at 7.9 psi

Yes, I pressurize to 12 psi using makeup valve near expansion tank. No, it never drops to 0. At 6.8 psi, boiler locks out. I never seen it drop lower. Once I add water, boiler wakes up and restores operation in few minutes. Overnight, pressure drops from 12.4 psi to about 7.9 psi, every night. Boiler room cools down from 74F to 68F. Yep, I can isolate the expansion tank. Should I?

hot_rod

How long has this system been running? It could be still purging air out, so pressure drops and fill water needs to be added.

Maybe run a few days with the fill valve left open so water replaces air that purges out

Got a pic of the boiler piping, does it have an air separator near the boiler?

GeneBA

hot_rod said:

How long has this system been running? It could be still purging air out, so pressure drops and fill water needs to be added. Maybe run a few days with the fill valve left open so water replaces air that purges out Got a pic of the boiler piping, does it have an air separator near the boiler?

Yes, it does have air separator. System is up for a week. I’ll try to replace pressure reducing valve and then maybe check on relief valve, backflow preventer valve. running out of ideas.

hot_rod

Any water trickling out of the backflow vent line? It debris was stuck in the second check, it cold be leaking a small amount down a drain.

No water leaking out of the condensate line when the boiler is off?

The BFD vent line really should not be tied into the relief valve discharge line, but…

Is the fill valve not working properly? It should be set the same as the expansion tank pre charge pressure to maintain say 12 psi

GeneBA

hot_rod said:

Any water trickling out of the backflow vent line? It debris was stuck in the second check, it cold be leaking a small amount down a drain. No water leaking out of the condensate line when the boiler is off? The BFD vent line really should not be tied into the relief valve discharge line, but… Is the fill valve not working properly? It should be set the same as the expansion tank pre charge pressure to maintain say 12 psi

This may sound funny. I pulled hard on the fill vavle yesterday. It stopped working, just hissing a bit when trying to add water. Well, pressure has stabilized, about 11.4 psi all day. Is it really possible.. fill valve can't leak back because there presumably 50 psi on street side of it. 

yes, I told contractor the same thing about tying relief valve line and BFD exhaust.

hot_rod

It really depends on the fill valve brand and model
Caleffi 573 has a check in the discharge

It the same check as in backflow devices. So with the Caleffi combo fill back flow you have 3 checks in a row protecting against backflow. In some markets, globally, the check in the fill valve passes as backflow protection.


Some Watts has a rubber flapper check on the discharge

HomerJSmith

You can check out the Double Check Backflow, Fill Valve, and Ex-tank by bringing the pressure up to 12psi when the boiler is cooled down and close the ball valve between the air sep and the Ex-tank and monitor the pressure for a day. You won't have any heat from the boiler for that time, but it would give you an idea if those 3 components are the source of your problem. If the pressure continues to decline look elsewhere.

I assume that the air charge (psi) on the Ex-tank is the same as the cold water fill valve setting. Is it?

Is the cap on the air vent on top of the air vent adapter on top of the boiler, if you have one, loose. No trapped air in the HX? What is the highest pressure reading when the boiler is operating for a while? I am thinking of the pressure differential between a cold boiler and a hot boiler.

exqheat

Would the air separator be more effective higher in the system piping?