NCB-240/130H Boiler Exhaust Leak

[dave_075]

Hello,
A few weeks ago, my old Navien CH-240 ASME combi boiler failed, and I had it replaced with a Navien NCB-240/130H, which I understood to be the closest replacement model. During installation, the installer reused the existing 3-inch PVC air intake and exhaust vents, adapting them to the 2-inch pipes required by the NCB-240/130H using compression fittings.

Initially, the system operated without issues for a few days. However, I noticed water accumulating on top of the unit, appearing to originate from the joints between the PVC fittings. The installer returned and applied glue to the joints, which temporarily resolved the issue. A few hours later, water began dripping from the exhaust collar around the metal clamp securing it to the exhaust vent. The installer attempted another fix by applying some sort of a sealant/glue and re-tightening the clamp, but the leak persists, particularly when the floor heating is active.

I’ve cleaned the condensate trap and drain line and confirmed there are no obstructions or debris in the exhaust line. The boiler display shows no error messages.

Could you provide guidance on resolving this issue? Would replacing the exhaust system entirely address the problem, or could the issue stem from another source? Any advice or recommendations would be greatly appreciated. I am attaching some pictures of the exhaust vent for reference:



Thank you for your assistance.

Dave

 

[GReynolds929]

If the joints were properly solvent welded there won't be leaks. Did the installer just put cement around the outside of the fittings, or did he take them apart and apply to both parts before reassembling. I would probably start over at this point since it's still leaking, and just redo it all in 2".

 

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[Breplum]

It is just bad luck on the installers part that they didn't glue something properly. It is their fault, cost to make right should be on them. The plastic round shield that Navien ships with water heater units.
Many plumbers have excess of these flanges and are happy to offload. For the cost of postage I can mail you one or two.