Navien 210s heavy draining at condensate drain

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Navien 210s tankless water heater condensate draining constantly

I have a navien 210s tankless water heater. Last week noticed a heavy drip from the condensate line and replaced the o ring on the flow sensor I let from the “emergency kit” inside the unit. That stopped the drip

This week, the unit began to have a heavy flow of water like a faucet from the condensate drain. Inspected same o ring and all was good. Contacted tech support and had me do the same and then said it was a bad heat exchanger.

As soon as I turn on the cold water supply it drains right out through the condensate drain

I sent in warranty form with papers and they denied the claim due to “improper venting” the previous installer did not vent as per instruction sheet.

Before I purchase a new unit what else would cause this ? Is there anything else I can trouble shoot ?


Licensed plumbing contractor
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San Francisco Bay Area
With normal installation, modern Navien units are amongst the best. They are often the only brand many plumbers/contractors choose. The heat exchanger is stainless steel and normally lasts forever if everything is installed properly, which isn't difficult.
How improper was the venting for your unit. It is hard for me to imagine installer not getting such simple stuff right.

We only recommend A2 series, as the internal pump and insulated mini-tank up the performance for getting hot water immediately out of the unit, instead of waiting for water to heat up inside first.
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