What Does Error Code E91 Mean on a Siemens Washing Machine?
Power cycle the machine by switching it off at the wall socket, waiting 5 minutes, then switching it back on and starting a new programme — this clears temporary communication errors in the majority of E91 cases (takes about 5 minutes).
Fault description
Error code E91 points to a breakdown in communication between the internal circuit boards inside your Siemens washing machine. Modern washing machines rely on multiple electronic control modules talking to each other constantly — the main control board, the motor control board, and the user interface board all exchange signals throughout every wash cycle. When that communication breaks down, the machine raises E91 and typically stops mid-cycle or refuses to start.
When E91 appears, you may notice the drum has stopped moving, the display is frozen, or the machine is unresponsive to button presses. In some cases the machine will attempt to restart itself and fail repeatedly. The fault can be intermittent at first, appearing occasionally before becoming permanent as an underlying issue worsens.
The good news is that a significant proportion of E91 errors are caused by temporary software glitches or loose wiring rather than a failed board, so there are several straightforward checks worth trying before spending money on parts or a call-out.
Causes
- Temporary software or firmware glitch — A momentary power fluctuation or software hang can cause the control boards to lose sync with each other. This is the most common cause and is often resolved by a simple power cycle.
- Loose or corroded wiring harness connector — The ribbon cables and plug connectors linking the main PCB to the motor board or display module can work loose over time due to vibration. A poor connection interrupts the data signal and triggers E91.
- Faulty main control board (PCB) — If the main PCB has suffered component failure — often due to a power surge or age-related wear — it may be unable to send or receive communication signals reliably. This typically requires board replacement.
- Faulty motor control module — The motor control board communicates with the main PCB to report drum speed and direction. A failure in this module can cause E91 even if the main board itself is functioning correctly.
- Damaged or faulty user interface board — The display and button panel has its own small circuit board that communicates with the main PCB. Physical damage, moisture ingress, or component failure here can disrupt the communication bus and raise E91.
- Power supply instability — Inconsistent mains voltage or a failing suppressor capacitor on the power supply circuit can cause intermittent communication errors between boards. This is more likely in older machines or properties with unstable electricity supply.
Step-by-Step Fix
- 1
Power cycle the washing machine
Turn the machine off using the power button, then switch it off at the wall socket. Leave it unplugged for at least 5 minutes to allow the capacitors on the control boards to fully discharge. Plug it back in, switch on at the wall, and attempt to start a new programme. This clears temporary communication faults in many cases.
- 2
Check the mains supply and socket
Try plugging the machine into a different wall socket if possible, or test the current socket with another appliance. Avoid using extension leads, as voltage drop can cause board instability. If your home has recently experienced a power cut or surge, check your consumer unit for any tripped breakers.
- 3
Inspect the door and drum for obstructions
Occasionally a mechanical fault — such as a jammed drum or a door that hasn't latched properly — can cause the machine to report a communication error as a secondary symptom. Open the door, check nothing is caught in the drum seal, and ensure the door clicks firmly shut before restarting.
- 4
Check the wiring harness connectors (if comfortable doing so)
Disconnect the machine from the mains before opening the back or top panel. Locate the ribbon cables and multi-pin connectors running between the main PCB, motor module, and display board. Press each connector firmly to reseat it. Look for any signs of corrosion, burn marks, or physical damage on the connectors. Reconnect the panel and test the machine.
- 5
Run a diagnostic or reset programme
Some Siemens models allow you to enter a service diagnostic mode by holding specific button combinations — consult your model's user manual or the Siemens support website for the exact sequence for your machine. Running a diagnostic can confirm which board is reporting the fault and may reset the error log if the underlying issue has been resolved.
- 6
Test with a different wash programme
If the machine starts after the power cycle, try a short programme such as a quick wash or rinse cycle rather than a full programme. If E91 only appears on certain programmes, this can help narrow down whether the fault is linked to a specific function or board.
- 7
Identify and replace the faulty board
If E91 persists after all the above steps, one of the control boards will need to be replaced. Note the exact model number from the label inside the door frame before ordering parts. If you are not confident working with electronics, this step is best handed to a service technician who can test each board individually before replacing.
Affected models
Select your model to see its full troubleshooting page.
When to call a service technician
If E91 returns immediately after a power cycle, or if the machine is completely unresponsive with a blank display, the fault is unlikely to be a simple software glitch. These symptoms suggest a hardware failure on one of the control boards that cannot be resolved without electronic testing equipment and, in most cases, a replacement part.
You should also contact a service technician if you notice any burn smell coming from the machine, visible scorch marks on connectors or boards, or if the machine trips your household circuit breaker when switched on. These are signs of a more serious electrical fault that should not be investigated without professional training.
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Frequently Asked Questions
Will a power cycle always fix error E91 on a Siemens washing machine?
A power cycle fixes E91 in a significant number of cases where the fault is caused by a temporary software glitch or a brief communication dropout between boards. However, if the error returns after the machine has been reset, or appears every time a cycle is started, there is likely an underlying hardware fault that needs further investigation.
Can I still use my washing machine if E91 keeps coming back?
It is not advisable to continue using the machine if E91 is recurring. A persistent communication fault means the machine's control systems are not operating reliably, which could lead to incorrect water levels, uncontrolled drum speeds, or the machine failing to stop at the end of a cycle. It is safer to have the fault diagnosed before continuing regular use.
How much does it cost to replace a Siemens washing machine PCB?
The cost of a replacement main PCB for a Siemens washing machine typically ranges from £60 to £180 for the part alone, depending on the model. Labour charges from a service technician will add to this. In some cases, a motor control module or interface board is the faulty component and may cost less to replace than the main board.
Is error E91 covered under Siemens warranty?
If your machine is within its standard manufacturer warranty period, a PCB communication fault such as E91 should be covered provided the fault is not the result of misuse or external damage. Contact Siemens customer support with your model number and proof of purchase to arrange a warranty assessment. Extended warranties from retailers may also cover this type of fault.
Could a power surge have caused my Siemens washing machine to show E91?
Yes, a power surge is a known cause of PCB communication faults. A sudden spike in mains voltage can damage components on the control boards, causing them to fail partially or intermittently. If E91 appeared shortly after a storm, power cut, or other electrical event in your home, it is worth mentioning this to a service technician as it helps narrow down which board is likely affected.