Any painters/decorators here?

I am a DIYer/bodger rather than a painter/decorator, but as no one else has replied ...

Are you re-painting because some of the paintwork has already flaked away? In that case the rest will peel off sooner rather than later in my experience, and if you try to get away with priming over the remaining paintwork you'll only have to do the job again, properly, next year.

If the existing paintwork had been OK, and you're just re-painting for cosmetic reasons, then maybe you'll get away with leaving the existing paint in place for a while.

My eventual solution to the fascia-board re-painting problem was to pay a roofer to replace them with PVC ones. I don't care what people say, quite frankly the modern grain-effect ones look more like wood than real wood does. A bit like Karndean floorboards in that respect. Worth every penny in terms of saving in time and general aggravation for maintenance.

Thanx for your /advice/reply screaming.  Cosmetic reasons really.

Make sure you use a good quality primer, Dulux Trade super grip primer works great on aged gloss, not cheap but worth it.

You've already done the hard essential bit abrading (sanding) the surface. Are you happy the surface is clean and dust free? if not wash with sugar soap and allow to dry thoroughly then prime. The top coat(s) will be a breeze

Btw,keep away from screwfix 'No Nonsense' fillers and paints, pure crap.

i agree with screaming

As already pointed out, surface preparation is a pre-requisite to the achievement of a long-lasting quality finish.
It is a task, however, that is rarely treated with the importance and priority it deserves.

OP has not said where the boards are and if it’s a ladders job , if they are vertical or horizontal or both ,what material they are made of and what width and length they are .How long he intends staying in the property ect . Know a few people who have replaced in plastic but coated metal either zinc or plastic seems popular these days in preparing for a maintenance free home .In Scotland wood can’t be used on new builds I think but for some reason often the timber that is used to repair older houses  is cheap ply  ,if it’s not too wide I would replace with decent wood ,pre treat and it will be good for 20 year . If it’s up high prob best to get someone in ,not worth falling off a ladder imo .simple jobs off a ladder are a pain . If it’s over 16ft ...swerve imo

Agree bnb ladders a a real no no. If doing it yourself then hire a tower.

brush on a good paint stripper ,,  [ not a cheap one [,,then sand paper  back to the wood ,, hope this helps,,