Rheem Water Heater Error 5 — Air Intake Blockage Fix

What Does This Error Mean?

Error 5 on a Rheem tankless heater is an air supply problem.
The unit can't pull enough combustion air, or the exhaust isn't venting properly.
Most often the intake or exhaust pipe outside has a bird's nest, leaves, or snow blocking it.
Walk outside and inspect both pipes — clear any obstruction and the unit usually restarts on its own.

Affected Models

Rheem RTGH series
Rheem RTG-95
Rheem RTGH-95DVLN
Rheem Performance Platinum tankless

Common Causes

Bird nest in the air intake or exhaust pipe
Leaves or debris blocking the exterior vent termination
Snow or ice covering the vent in winter
Vent pipe collapsed inside a wall (older installs)
Air filter at the unit clogged with lint

How to Fix It

Find the vent termination outside.

Trace the exhaust and intake pipes from the heater to where they exit the house.
Most concentric vents come out the side of the house as a single pipe with two openings (inner exhaust, outer intake).
Some installations use two separate pipes.
Clear visible debris.

Look at both openings.
Birds love these warm pipes for nesting — clear any nest material with gloves and a stick.
Clear snow buildup if it's winter.
Wasps sometimes build nests inside; cover the openings with vent screens after clearing if you live in an area where this is recurring.
Check for collapsed vent pipe.

If the outside is clear and Error 5 persists, the vent pipe inside the wall may have collapsed or come apart at a joint.
Listen for hissing or wind noise near the vent.
This is a service issue — the venting needs inspection by a licensed installer.
Inspect the unit's air filter.

Some Rheem tankless models have a small air filter at the bottom of the unit.
If yours does, pull it out and tap dust off.
Replace if it's heavily clogged.
Reinstall and try restarting the heater.
Reset the unit.

Press the on/off button to power down.
Wait 30 seconds.
Power back on.
Run a hot tap.
If Error 5 returns within seconds and you've cleared everything visible, call a licensed installer — there's an internal venting issue that needs diagnosis.

Frequently Asked Questions

Why does Error 5 happen most in winter?

Snow and ice accumulate at the vent termination during winter storms.
Especially in lake-effect snow or coastal climates, drifts can completely cover side-wall vents within hours.
Most installers recommend a vent extension or a snow shield in those climates to prevent recurrence.

Can I run the heater with Error 5?

No — and you shouldn't try to bypass it.
Error 5 means combustion is restricted, which can lead to incomplete burning and carbon monoxide.
The protection exists for safety.
Don't run the unit until the airflow path is clear.