Thanks, that's not it unfortunately. The filter I bought had these instructions:

switch off the control panel
press down button for 8 seconds (will beep after 3 but keep going for the full 8 seconds)
0.2 is displayed in the roof and -20 is displayed in the house
push on on/off button and a 1 or a 5 will be displayed
push on on/off button again & again to cycle though the numbers until you come back to the 1 or 5 being displayed again.
push the function button to confirm

Only thing is there's no down button on this controller

There must be some combination of button presses??

Did you try asking the manufacturer? Seems like a reasonable first step.

Hmmm... we have one of these and not too sure what you mean when you say "filter light" can you details exactly which light you are talking about in the picture

Cheers everyone for your replies

Its the 'Replace Filter' Light that is flashing

I contacted HRV but got frustrated as they were trying to up sell me the new model - so I thought Id ask on here.

The 2 online manuals doesn't say how to do it unfortunately

I'll email the supplier of the new filter - see what happens

Thanks once again everyone

I got a replacement aftermarket filter from Ventsure for my mum's HRV. Their instruction page has quite a bit of info. Her controller was different to yours.

Thanks everyone, will try the suggestions this weekend ... (its installed at a rental property)

Piece of duct tape as previously mentioned or ignore it, it's not as though its a check engine light and the world will end.