Glow Worm Compact 80 P - pilot light trips off?

Initially, relay constantly clicking in and out, boiler flaming up and down; then pilot tripped out and once relit kept tripping after 20-25 mins on heating setting. PCB replaced - signs of arcing in and around a relay. No more clicking but pilot problem persisted - definite switch sound as pilot goes out. Thermister (looked manky) and thermocouple replaced; whole system drained and flushed. TRV on one rad replaced with manual valve - now have 2 of these - believe needed to act as sink for getting rid of excess heat in system to prevent boiler overheat. All rads getting red hot. Problem persists, though pilot remains lit for 45mins - 1hr. The only way to stop this is by having all rad TRVs set to max - pilot then stays alight. Been charged £400 so far but still not sorted. Seems to a bonehead like me that the boiler is overheating and a safety switch is cutting the gas supply. Fan working fine, by the way. Any ideas gratefully received!

Mike
January 2008