Exhaust Blockage / Condensate Blockage
The exhaust system or condensate drain is blocked. On Navien boilers this is the specific code for a blocked or frozen condensate pipe — the most common winter fault.
Code 110 is Navien's condensate blockage code. In winter this is almost always a frozen condensate drain pipe — the most common Navien winter fault.
Step-by-Step Fix Guide
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Step 1
Locate the Navien condensate outlet (usually at the bottom-rear of the boiler)
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Step 2
In cold weather, check if the condensate pipe or drain is frozen — pour warm water over the frozen section
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Step 3
Wait for the blockage to clear
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Step 4
Reset the boiler
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Step 5
If fault persists, call a Gas Safe engineer to inspect the condensate system
Work on gas appliances must be carried out by a Gas Safe registered engineer. The steps above cover safe checks a homeowner can perform - any internal component replacement requires a qualified professional. If in doubt, always call an engineer.