potterton profile 80e?

Call for heat - Fan runs - pressure switch detects fan = OK - opens valve to pilot and ignites it - if pilot hot main gas valve opens. If pilot not hot system shuts off gas.

See these URLs

http://www.howtomendit.com/answers.php?id=26383

and

http://kaijaks.co.uk/blog/nick/2008/02/10/dodgy-old-boiler

Peccavi
November 2008

Could be pcb,but you cant afford to guess as these are expensive.

Tony S
October 2008