A tankless water heater needs two types of venting—air intake for combustion, and exhaust for evacuating heat and gasses after combustion occurs. The water heater will have a power vent system, which intakes air from indoors but vents outdoors, or a direct vent system that pulls in outside air as well as venting outside. If you have errors that occur with the water heater due to vent issues, the type of venting along with one of the following three causes is likely the root of the problem.
1. Check for Vent Damage
The most obvious reason for poor venting is damage to your vents. First, make sure the connections between the vents and the tankless unit itself are sound with no air leaks. Then, check the indoor vent, if applicable, for holes or cracks. The next step is to check the exterior vents for damage that could impact their ability to drawn in or expel air. It's rare for vents to become so damaged that they pass through the walls of your home unless you have had recent renovations that could have penetrated through a wall and into the vent.
2. Verify Interior Intake Clearance
Intake clearance can be a real issue, particularly with a power vent system. Many people place the tankless water heater in a cabinet or closet so it is out of sight. Since these heaters are so much smaller than a tank heater, it can be tempting to place them in a very small space so you can maximize storage for other things. Unfortunately, this can mean there is less air circulation around the intake and the unit may shut down due to poor combustion. The owner's manual for the heater should detail how much clearance is necessary for your intake. It's also a good idea to avoid storing any items in the water heater cabinet.
3. Inspect Exterior Vents
Exterior vents and intakes aren't immune to blockages, either. Ideally, these vents should have screening or a vent cap on top to keep out debris and pests. Sometimes, though, these caps become damaged or lost due to wind or hail. Leaves and debris can get inside and block the vent. Bird, squirrel, or insect nests can also lead to a blockage. Clearing out the vent and replacing the vent cap will solve the issue.
Contact a tankless water heater repair service if you need more assistance with your heater's venting.