When a Bosch washer flashes Er:08, it’s telling you the water-heating cycle took too long—usually because the heater stayed on when it shouldn’t. Think of it like a kettle that never stops boiling: the control expects the temperature to climb and then the heater to switch off, but something in the circuit keeps feeding power. The good news? You can track this down with a calm, step-by-step approach and a couple of basic checks.

First things first: make it safe

Unplug the washer and give it a minute for any residual charge to bleed off. If the machine is built in, pull it forward enough for safe access and make sure the floor is dry. No water, no power, no surprises.

What usually causes Er:08?

Two culprits show up again and again. The first is the heating element itself—if it’s shorted to the metal tub or its sheath is damaged, it can continue heating regardless of commands. The second is the control module’s heater relay, which can weld itself stuck in the ON position. Less common, but still possible, is chafed wiring that effectively bypasses normal control.

How to diagnose it like a pro

Start with the simple visual check. Remove the back panel, find the heater (it sits in the lower part of the tub), and look for burnt spots, bulges, or corrosion on the terminals. A heater that’s physically damaged is a strong sign you’ve found the problem. If you have a multimeter, you can go one step further: disconnect the heater’s wires and measure resistance between each terminal and the metal chassis. Any reading other than “open” (infinite resistance) to ground means the element is leaking to the cabinet—replace it.

If the heater looks clean and tests healthy, turn your attention to the control module. Here, what you’re looking for is a relay that’s failed closed. You won’t always see scorching or damage, but a board that smells burnt or shows darkened spots around the relay is suspect. In practice, if the heater checks out and the wiring isn’t shorted, the control is your most likely fix.

Repairs that actually resolve Er:08

A damaged heater needs to go—don’t try to “nurse it along.” A shorted element can trip breakers, overheat water, and stress the electronics. Fit the correct OEM-spec replacement and reseat the gasket carefully so you don’t create a leak.

If the heater passes inspection, replace the control module (or have a qualified tech replace the relay if they offer board-level repair). Swapping in a known-good control restores proper heater switching and clears the error once the system retests the heat cycle.

Wiring and “sneaky” shorts

While you’re in there, follow the heater wiring harness from the element to the control. Look for insulation rubbed thin where the loom passes over sharp edges or brackets. Any copper peeking through is a potential short. Tape isn’t a fix here—repair or replace the harness section so you’re not sending stray power down the line.

After the fix: verify the outcome

Once you’ve replaced the faulty part, reassemble the panels, plug the washer in, and run a warm or hot program with no load. You want to see a normal heat-up (no error during the cycle) and a proper finish. If your model supports diagnostics, run the self-test; clearing stored faults and watching for a clean pass gives extra confidence.

Prevention so you don’t meet Er:08 again

Hard water and heavy detergent use can layer scale on the heater, making it run hotter and longer. Use the right detergent dose, run an occasional maintenance cycle with a descaler if your water is mineral-rich, and don’t overload the drum (overloads keep water from circulating, which slows heating). Good ventilation around the machine also helps electronics live longer.

When to call a technician

If you’re not comfortable removing panels or using a multimeter, there’s no shame in calling a pro—especially for control-board work. Persistent Er:08 after a new heater, signs of scorched wiring, or tripping breakers are all “stop and phone it in” moments. A certified Bosch tech can confirm the fault path quickly and protect the rest of the machine from collateral damage.

Unplug for safety, inspect and test the heater first, replace it if it’s shorted or damaged; if the heater and wiring are good, the control module (stuck relay) is the likely fix. After repairs, run a hot cycle to confirm normal heating and clear the code. Keep scale in check and loads reasonable to avoid repeat issues.