The boiler installation and service manual has a fault finding chart in the back - p26.
I just found this - may still be current...
Potterton were taken over in 1996 or thereabouts and are now called baxi potterton. You can obtain a manual for your potterton boiler by calling their after sales technical support on 0870 6060780 ... they will give you a phone number and if you quote your boiler make, the paperwork appears in the post within 3-5 days.
Baxi Potterton
Brooks House
Coventry Road
Warwick
CV34 4LL
Peccavi, February 2009
