I have one of these controls on a new riello burner,and I've watched it go through a cycle and then after everything shut down the thing goes off on safety. I know that it monitors for after fire, but that should be 12 sec. before it locks out. The burner ran, fired without a hitch, boiler satisfied, post purged, then returned to it's starting mark and a couple of seconds later clicked off on safety. The burner is going off at least once a day, same spot( start up triangle). Any hints on how to check these things out?
Bluenose - this control checks for flame at both ends of the cycle - and if you have bright lights above the burner it is enough to put the control in alarm mode. While you didn't say what type of boiler - cover all observation ports to the combustion area. If this doesn't do the trick - then in all likelihood in the flame safeguard needs replacement. It is the same control used on many other burners like the Weishapt etc but may have a different designation as it's on a riello. Hope this helps