Combi boiler - no baseboard heat, DWH working perfectly

domnolan

Hi all,

I installed a Navien NCB 240-130H Combi boiler to after the indirect hot water tank went on us back in June. Since the install the Domestic hot water has worked perfectly, but this is the first week of colder weather and this morning I noticed the house wasn’t warming up and the baseboards were cold.

The manifold is hot up until the circulation pump inlet but is cold on the outlet side. Pump is installed on supply side. And the motor is warm.

I opened the drain on the return side of the zone (currently only run one zone, but built the manifold to support three for future expansion) and the was no spitting or sputtering. I drain about 4-5 3gallon buckets worth this way before I closed the isolation valve after the drain. I ran out of time before I had to head to work and only removed another 2 buckets. Still no sputtering but I did notice some air coming out the vent at the top of the line. 

I’m a power plant operator, not a Plummer, so I have the basic understanding of theory, but I’m working on circulation pumps the size of Mack trucks vs the size of my had so there’s definitely so nuance to the system I don’t understand. 

Would the little bit of air I was hearing from the vent be preventing all flow through the hydronic system even though there are vents and reliefs throughout the system? Or is there another cause you could think of that would be preventing the hot water in the manifold from flowing through the circulation pump and piping? I don’t hear and cavitation happening in the pump. Manifold is hot from the outlet of the magnetic filter on the return side -> boiler-> supply manifold -> circulation pump inlet / then it’s cold.

Pressure on system showed about 21 psi before drain, 14ish psi while draining, and stabilized around 17 psi when realigned to normal operating configuration. Heat is set to 180 F monitored on the supply side (switch to sensing from return side made no difference.) The boiler would kick on for 5-20 seconds intermittently when temp dropped to 175 F and stopped at 181 F.

Should I (only) continue trying to vent more air when I get home, or are there any other troubleshooting steps you could think of? I tapped the three-way valve in the boiler a bit, with no luck.

Thanks for any help you can offer,
-Dom

(I apologize, This might accidentally be a re worded repost. I attempted to edit my first discussion and it completely disappeared.)

GroundUp

Simply put, you have an airlock that needs to be purged either with domestic pressure or an external pump. Also I sincerely hope that flue is not just taped together as it appears. That boiler should have been installed and started up by a professional.

hot_rod

Turn off the whithe handle ball valve when you purge?

Power on the circulator?

Could be something stuck in the circulator. You have isolation valves, turn off, the pull the 4 hex bolts out, 5/16 nut driver I believe. set the pump on the piping and power it on to see if it spins freely.

I would close off that high auto vent once you get it going, depend on the Spirovent to clean out any small air.

domnolan

Also I sincerely hope that flue is not just taped together as it appears. That boiler should have been installed and started up by a professional.

No, the flue was properly sealed with the pvc cement recommended (note the streams of purple from over applying) - the tape was added after just for an extra barrier. There’s a carbon monoxide detector within 10ft of it, and I verified no leaks with a Ventis Mx-4.
A “professional” who went through Navien’s training installed my father’s and it’s one of the hackiest jobs I’ve ever seen. The relief valve piping ended about 4ft off the ground, the only domestic supply shut off was on the other side of a home, and it had no additional outlet or shut off switch at the unit, only the the breaker at the other side of the basement would shut off power. Between my 6 years of aerospace maintenance and almost ten operating a power plant, I can safely say I trust the installation is adequate. Like I stated, I understand the theory of the system, but the scale I’m used to is several hundred times the size and output. I’m just looking for troubleshooting tips for what seems to be a pretty basic issue. A water lock makes sense and is what I mainly suspect, but with no water hammering, the pump not caveating, and getting normal flow through the drain without any spitting or sputtering I wanted to make sure I’m not chasing the wrong issue before going down a rabbit hole.

domnolan

Turn off the whithe handle ball valve when you purge? Power on the circulator? Could be something stuck in the circulator. You have isolation valves, turn off, the pull the 4 hex bolts out, 5/16 nut driver I believe. set the pump on the piping and power it on to see if it spins freely. I would close off that high auto vent once you get it going, depend on the Spirovent to clean out any small air.

The air only began venting from that high point auto vent after I isolated the white ball valve, that was what lead me posting here because I had assumed the Spirovent would have been sufficient at deaerating, so I’m glad I wasn’t too far off thinking it’s probably an air pocket.

I’ll save pulling the pump until I’m positive I fully purged everything. Thanks for the advice!

GroundUp

Did that experience put a combustion analyzer in your hand and make necessary adjustments to the gas valve when you started up the boiler?

I can't see where you're adding water, but it needs to have some velocity in order to push out a bubble in most cases. An auto-feeder isn't always enough. Just because water is coming out a low point drain doesn't mean that there is no air- this is a very common issue. If you can get some actual domestic pressure or an external pump connected to muster up that velocity, you should be just fine. The problem is that a regular circulator, especially that one, doesn't generate enough head pressure to push air bubbles of any size.

CPHNed

Is the diverter motor/valve working properly?

HeatingDanny

I'm just reading through these posts. Unfortunately your "experienced" installer who went to Navien training must have been sleeping through class. First, Navien strongly recommends NO black pipe on an installation. Should be all copper. Also I'm looking at the check valve installed after the circulator. That is a swing check, which should never be installed in the vertical position. Its designed to be installed in a horizontal position because the flapper is made of brass which can be on the heavy side when installed vertically. When we're talking 15 - 20 psi, there may not be enough force to keep it in the open position.
I can't tell from the picture, make sure that the arrow on the circulator is pointed upwards and the same goes for that check valve that was installed.
If the pipe was glued at all the joints there is no need ever for aluminum tape.
One last thing, 4 shut offs on an incoming gas line? I don't see how that makes any sense. Very messy gas piping job.

hot_rod

Swing checks depend on a pressure differential to seal, and sometimes even close properly.

The pressure in a closed hydronic system is the same on both sides of a check when the circ is not running. There is no pressure differential.

Plus the Cv is generally too high for hydronics, so the flow may not open the swing completely, the swing floats around in limbo

Hydromatt

Unfortunately there are a lot of professional hacks out there! Your install looks great. These boilers are finicky so a combustion analysis is important but not related to your question.
from what you described there is definitely no flow through the system.
A warm circ could just be from migrating heat. A red hot circ is usually a gonner and should be replaced. These Lil circulators can handle a short time of dry fire before they burn up. Taco makes replacement cartridges.
If it is cavitating you can usually hear it gurgling.

Return ball valve closed while purging? Exercise purge drain while purging to allow pressure buildup. Sometimes it helps to purge while the system is running.

Like hot rod said, check power to corc. Wiring. System circulator settings.