Gulfstream tripping out on boiler over temp

The boiler starts up, runs for approx 10 seconds before you start to hear steam generating in the heat exchanger and then venting out of the release at the top left hand side. I am guessing the pump is not circulating the water so it is overheating in the exchange? There does not appear to be any fuse or protection on the pump supplies, are they running at 230v or less?

Any help / guidance appreciated