Bosch Dishwasher E:04: Backup Heater Relay Failed Its Test

What E:04 means

A newer Bosch can show E:04 when heating stops or a cycle heats poorly. Inside is a spare relay that exists only to cut heater power if the main relay sticks, and the control tests it periodically. E:04 says that test failed. Current leaking from the heat pump heater or the zeolite heater to ground can set the same code, since that is the very leakage the spare relay guards against.

Common causes of E:04

Spare heater relay on the power module has failed
Heat pump heater leaking current to ground
Zeolite drying heater leaking current to ground

✓ One safe check you can try

No owner test applies, because E:04 concerns the backup guarding the heater circuit. 1. Switch the breaker off. 2. Resist the urge to reset and run it again to see. 3. Book a diagnosis, and mention any tingle from the door or a tripped breaker when you call.

! Why to stop there

The backup relay exists for the day the main one fails, so running the machine without knowing its state may mean a safeguard is missing.
Separating a relay failure from a leaking heater takes an insulation tester, not a basic voltmeter.
Heaters of this kind are replaced whole, so a tear-down rarely salvages anything.

Opening a panel yourself does not automatically cancel a manufacturer warranty, but it can cause accidental damage, and some manufacturers set their own service conditions. Check your warranty terms, or ask us, before deciding.

→Same appliance

Other Dishwasher codes

E:01Bosch Dishwasher E:01: Cycle Ended Early, Heater Relay or Pump Unconfirmed E:30Bosch Dishwasher E:30, Voltage Too High and the Machine Shut Down E:31Water in the Zeolite Container - Bosch Dishwasher E:31 FBosch Dishwasher F on an Older Display (Water Filling) 2HBosch Dishwasher 2H: Long Cycle Warning on Older Displays 1Bosch Dishwasher Service Test Result 1: Aqua Sensor 2Bosch Dishwasher Service Test Result 2: Heating Group 4Bosch Dishwasher Service Test Result 4: Water Filling

E:04E:04 questions

How is E:04 different from E:02?

E:02 points to the primary heater relay or the heaters, while E:04 points to the backup relay that watches over them. Leakage to ground can set off either, so we test the circuit instead of trusting the code alone.

Can a reset make the machine safe again?

No. A reset hides the message but does not repair a failed safety relay or a leaking heater. We recommend waiting for a proper diagnosis.

What does the repair cost?

It depends on whether the module or a heater is needed. We tell you the price in writing before we start, and the finished work carries a 30-day workmanship warranty.