Bosch EA Error Code — What It Means
The EA code means your Bosch tankless water heater is not detecting flame ionization during a heat demand. In simpler terms, the unit tries to ignite when you call for hot water but either fails to light the burner or cannot confirm that a flame is present. Water may flow through the heater but it stays cold because combustion never starts or the control doesn’t sense it.
This fault usually points to something interrupting the ignition or flame-sensing circuit. It can be as simple as a closed gas valve or air trapped in the line after recent service, or as involved as a corroded electrode, insufficient gas pressure, blocked venting, or moisture intrusion into the burner chamber. The heater will lock out and display EA until you identify and fix the root cause.
Common Causes
- Insufficient gas supply pressure or closed shutoff valve Natural gas models require at least 5 inches water column at high fire and a maximum of 14 inches supply pressure, and any manual gas cock left closed will prevent ignition entirely.
- Air trapped in the gas line After installation or gas service work, air can occupy the piping and prevent fuel from reaching the burner until it is purged by repeated ignition cycles.
- Dirty, corroded, or damaged ignition electrodes The spark electrode and flame sensor rod must be clean and properly seated with intact wiring (especially the two yellow braided-wire connectors) or the unit will not spark or confirm flame.
- Blocked or improperly installed venting and combustion air intake Obstructions, excessive equivalent vent length, or incorrect termination starve the burner of oxygen or prevent exhaust from leaving, stopping reliable combustion.
- Moisture intrusion or condensate backup Rain entering the vent termination, a plugged condensate trap, or water pooling in the burner compartment can short the ignition circuit and prevent flame detection.
- Faulty gas valve or incorrect drive voltage If the gas valve does not open when commanded (you should measure approximately 24 VDC across its leads during a call for heat), no fuel reaches the burner even when spark is present.
Step-by-Step Fix
- Confirm water flow demand by opening a hot-water tap and verifying that the heater display shows an active heat call before troubleshooting ignition components.
- Check all manual gas shutoff valves upstream of the heater and confirm they are fully open, then verify the nameplate fuel type matches your supply (natural gas or propane).
- Measure gas supply pressure with a manometer at the heater inlet during high fire to confirm it meets the minimum 5 inches water column for natural gas and does not exceed 14 inches maximum.
- Purge air from the gas line by resetting the heater and running several hot-water draw cycles if the unit was recently installed or the gas supply was interrupted.
- Inspect the ignition electrodes and flame sensor for corrosion, carbon buildup, cracks in the ceramic insulator, or loose yellow braided wires at the connector, and clean or replace as needed.
- Observe spark and flame through the sight window during ignition; if you see spark but no flame, measure voltage across the gas valve leads with water flowing to confirm approximately 24 VDC.
- Inspect vent and air-intake pipes for blockage, bird nests, ice, excessive length, or improper termination, and clear or correct any issues, then check that the condensate trap is not plugged and the burner area is dry.
Parts Often Needed
| Part | Notes |
|---|---|
| Ignition electrode and flame sensor assembly | Amazon | Order the assembly specific to your Bosch tankless model; includes ceramic insulators and yellow braided electrode cables. |
| Gas valve | Amazon | Replace if voltage is correct but the valve does not open or if combustion calibration cannot be restored after electrode and vent repairs. |
| Condensate trap kit | Amazon | Necessary if the existing trap is cracked, plugged with debris, or missing the water seal that prevents combustion gases from recirculating. |
When to Call a Pro
Call a licensed technician if you are uncomfortable working with gas connections, do not own a manometer and multimeter to measure supply pressure and valve voltage, or if the heater continues to show EA after you have verified gas supply, purged air, and cleaned the electrodes. Combustion appliance work requires proper tools and training. A pro can also perform a full combustion analysis with a flue-gas analyzer to verify air-fuel ratio, check for carbon monoxide spillage, and recalibrate the gas valve after any repair or conversion. If moisture intrusion is chronic or the burner tray shows corrosion, a technician can assess whether the vent termination meets code and whether internal components need replacement.