Problem solved , printer looks for lowest channel number so assigning the router a lower 2.4 GHz channel sorted it .Otherwise I would have had to give the power line extender a different SSID which cause issues with old iPad not connecting to strongest signal when moving around.

Sicog wrote

I have a cannon printer , 2ft away from router but it insists on connecting to the range extender 30 ft away resulting in 

a non functional WiFi strength .

I can set the printer back to the router , all is good , but after a turn off it reverts to extender .

On advice from Canon I changed the extender channel to a higher number than the printers .

That worked briefly then it reverted again .

Canon did hint at changing the SSID on the extender , but in the past that causes minor hassles with

some devices not switching seamlessly between the networks if you move around in the house .

Any suggestions please .

Official support says its for Canon the sort out .( They are having a think about it ) 

Thanks

  @Sicog