Rinnai code 10: air supply, exhaust or condensate blockage

Code 10 tells you the heater cannot move combustion air and exhaust properly. The fix is often outside the house at the vent, or at the condensate drain line.

Look at the intake and exhaust terminals on the outside wall or roof. Clear snow, ice, leaves or debris by hand and keep plants and stored items away from them.

Condensing models: check the condensate drain

On Rinnai SENSEI condensing heaters, a condensate line that is clogged or frozen backs water up into the trap inside the unit. The heater shuts down to prevent spillage and shows code 10. Check that the drain line runs freely, is not kinked and is not frozen.

Non-condensing models: inlet air filter

Some models have an air filter behind the front cover. A dirty filter restricts air. Your manual shows whether your model has one and how to reach it.

If the vent and drain are clear

Disconnected or damaged vent pipe, a vent run longer than the manual allows, a vent pipe crushed where it passes through the wall, a failing combustion fan, or debris between the heat exchanger fins can all trigger code 10. These need a technician.