Hi, I am trying to sort out problems on newly acquired 2008 Citroen Relay 2.2 hdi. The water in fuel sensor - is the sensor part of the fuel filter housing, or can the sensor be removed from the housing to replace it?

Also, the oil can service light is flashing, and I have just serviced it. Can anyone tell me the procedure to reset it please?

Thanks!

The water sensor, like the fuel temperature sensor, are part of the UFI filter housing. Both are not replaceable.
For resetting electronic functions you need an OBD-2 compliant device, either wired or bluetooth.
I recommend bluetooth because there are a lot of software packages on the market for tablets or smartphones.

Measure the resistance of the wif probe it's very unlikely to be faulty unless it's corroded. It's far more likely there is corrosion or water in the connectors / loom further down the line. Water ingress is very common. Disconnect the battery and check the ECU connectors for evidence of ingress.

Bluetooth adapter is very handy, on android alfaobd has a lot more fuclnctionality than the likes of torque. You can get adapters with a power switch that you can leave in situ until needed. Generic bluetooth will only do engine. If you need to work with airbag, abs, body computer a made in england obdkey can do those with alfaobd or you will need a laptop with alfaobd or multiecuscan and kkl cable with switches or kkl cable with adapter cables.

you have to replace the filter housing around £70 off ebay as the sensor is in the top part or I suppose you could change the top part if you got an old filter must be loads around