potterton envoy 40?

please could someone help me...i have a potterton envoy 40 condensing boiler....the boiler only runs for about 30 mins or 2hrs if i'm lucky...then up comes the flashing E error then i have to reset the boiler 5/6 times aday...last year it had a new gas valve ( which broke the bank ) when i first had this fault it said replace the controller thinking they meant the control board which i replaced ( costing an arm & leg ) it lasted afew days and the fault came back....after blowing £500 altogether i'm back where i started thank u for any help