ravenheat primary mk 1 heat only fault?

i was called to a customers boiler not working following new gas mains work in street. i reset the boiler and it fired first time, customer asked me to carry out safety check which i did on completion the boiler was cutting out after 10 secs and restarting without being reset, i contacted r/h technical and was advised to replace pilot burner which i did, this seemed to cure problem but boiler keeps locking out after 10 mins. gas pressure is fine and gas valve filter is clean. following fault finding in manual points to over heat stat? thanks stu