What Does Error Code F18 Mean on a Bosch Washing Machine?
Clean the detergent-solution pump filter (located behind the small access panel at the bottom front of the machine) by unscrewing it, removing any debris, and rinsing it under a tap — this resolves the majority of F18 errors and takes about 10 minutes.
Fault description
Error code F18 is Bosch's way of telling you that water is not leaving the drum fast enough — or at all. The machine monitors how long the drain cycle takes, and when it exceeds a set threshold, it stops the programme and displays F18 to protect the motor and drum bearings from running in standing water.
When this error appears, you will typically find the drum still full or partially full of water, and the door lock will remain engaged as a safety measure. The machine will not continue the cycle or allow you to open the door until the water level drops to a safe point.
The good news is that F18 is one of the most straightforward faults to resolve at home. In the vast majority of cases, the blockage is in the pump filter or the drainage hose — both of which are accessible without any specialist tools.
Causes
- Blocked pump filter — The pump filter traps lint, coins, hair grips, and other small items before they reach the drain pump. Over time this debris builds up and restricts water flow enough to trigger F18.
- Kinked or squashed drainage hose — If the machine has been pushed too close to the wall or the hose has been routed at a sharp angle, water cannot flow freely. Even a partial kink can slow drainage enough to cause a timeout error.
- Blocked or incorrectly positioned standpipe or sink outlet — The external drain point — whether a standpipe, under-sink trap, or utility sink — can become blocked with household debris. The hose outlet must also be positioned at the correct height (typically 60–100 cm) to prevent siphoning or back-pressure.
- Faulty or jammed drain pump — A small object such as a button or piece of glass can pass through the filter and jam the pump impeller. The pump motor may also fail electrically, preventing it from running at all.
- Wiring or control board fault — In less common cases, the connection between the main control board and the drain pump can develop a fault, meaning the pump receives no signal to run even though the drainage path is clear.
Step-by-Step Fix
- 1
Switch off and unplug the machine
Before doing anything else, turn the programme dial to off and unplug the machine from the wall socket. This is essential before accessing the pump filter. Place a few old towels on the floor in front of the machine to catch any water that spills out.
- 2
Drain residual water manually
Open the small access flap at the bottom front of the machine. You will see a short black emergency drain hose clipped next to the filter cap. Pull it out, remove the plug from its end, and let the water drain into a shallow bowl or tray. Refill the bowl as needed until the flow stops.
- 3
Remove and clean the pump filter
Turn the filter cap anti-clockwise slowly — it will still release a small amount of water, so keep your towels ready. Pull the filter out completely and rinse it under a running tap, removing all lint, coins, and debris. Also reach into the filter housing with your fingers and check for any objects lodged inside. Refit the filter firmly and close the access flap.
- 4
Check the drainage hose at the back of the machine
Pull the machine forward slightly and inspect the full length of the drainage hose. Look for kinks, tight bends, or any point where the hose is being compressed against the wall or cabinet. Straighten any kinks and ensure the hose has a gentle curve rather than a sharp angle.
- 5
Check the standpipe or external drain connection
Disconnect the hose from the standpipe or sink outlet and check for blockages at that end. Run some water from a tap into the standpipe to confirm it drains freely. Reconnect the hose and make sure it is inserted no more than 15 cm into the standpipe to avoid siphoning.
- 6
Plug in and run a short test cycle
Reconnect the power and select a short cotton or rinse-and-spin programme. Stay nearby and listen for the pump running during the drain phase — it should produce a steady hum. If the machine completes the cycle without displaying F18, the fault is resolved.
- 7
Listen for a jammed pump impeller
If F18 returns and you can hear the pump attempting to run but no water moves, a foreign object may be jamming the impeller. With the machine unplugged and water drained, remove the filter again and use a torch to look into the housing. Try turning the impeller gently with a finger — it should rotate freely. If it is stuck or you cannot free it, the pump will need to be replaced.
Affected models
Select your model to see its full troubleshooting page.
When to call a service technician
If you have cleaned the filter, straightened the hose, and confirmed the external drain is clear but F18 continues to appear, the drain pump itself is the most likely culprit. A pump that hums but does not move water, makes a grinding noise, or does not run at all will need to be replaced — this involves disconnecting internal wiring and hoses, and is best handled by a service technician.
You should also contact a service technician if the error code returns within a few washes after cleaning the filter, as this can point to a control board fault that is not sending the correct signal to the pump, or a wiring harness issue that requires diagnostic equipment to identify accurately.
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Frequently Asked Questions
Can I still open the door when F18 is showing?
Not immediately — the door lock stays engaged while there is water in the drum. Use the emergency drain hose behind the bottom access flap to remove the water first. Once the drum is empty, the door lock should release within a minute or two, or you can use the door release tab inside the access panel if your model has one.
How often should I clean the pump filter on a Bosch washing machine?
Bosch recommends checking the filter every few months under normal use. If you wash items that shed a lot of lint — pet bedding, fleece fabrics, or heavily soiled workwear — clean it monthly. A quick clean takes less than ten minutes and is the most reliable way to avoid F18 appearing.
Will F18 clear itself if I just restart the machine?
Occasionally a one-off slow drain caused by a temporary partial blockage will not reappear after a restart, but in most cases the underlying blockage is still present and the error will return. It is always worth cleaning the filter before restarting rather than hoping the fault resolves on its own.
Is F18 the same as E18 on Bosch machines?
Yes — some Bosch models display the fault as E18 rather than F18, but both codes refer to the same drainage timeout fault. The diagnosis and repair steps are identical regardless of which prefix your display shows.
How much does it cost to replace a Bosch washing machine drain pump?
A replacement drain pump for a Bosch washing machine typically costs between £20 and £50 for the part, depending on the model. If you are comfortable with basic appliance repairs, it is a job many homeowners tackle themselves using online guides. If you prefer to have a service technician fit it, expect to add a call-out and labour charge on top of the part cost.