This is from memory so apologies for any inaccuracies.
Firstly, you must not work on any gas appliance without being Corgi registered in the UK. This is the law and as such the following information is offered for information only and with no warranty either impled or otherwise...yada yada.
The Netaheat range is an automatic ignition boiler, the pilot is automaticically lit by an electronic ignition unit. first the fan comes on, pressurises the pressure switch and that tells the electronic unit to open the gas valve and start the spark for the pilot, if the pilot fails to light within a certain time (30 secs?) then the boiler will stop sparking. any one of these items failing will stop the boiler from igniting. As the unit is 25+ years old now the liklihood of obtaining spares is I would think quite slim. if you can hear ticking (the spark) then the gap should be checked by your heating engineer as this may be a simple and cheap fix.
HTH (even if it is a year late!)
G Butler (ex Potterton Tech support), December 2008
