Unfortunately Steinigke doesn't list the ballast or igniter in their web parts shop. If you do, the problem's probably downstream of the control electronics. Lamp power is switched by a relay - do you hear a clicking noise when you tell the fixture to strike? If not, there's a problem that may be unrelated to the ballast/igniter. With the fixture powered off, you can visually inspect the connections in the base and make sure nothing's worked its way loose, and even do continuity checks at either ends of connections to make sure a wire hasn't broken or come loose at some interconnect somewhere inside the light. With the fixture powered off, you should see a closed circuit across the terminals of the thermostat, it's designed to open up and disconnect power to the lamp if the fixture starts to overheat. There is a thermostat, visible on page 11 of that PDF, mounted to the lamp housing assembly.

There does seem to be two revisions of the fixture, so you might need to figure out which one you have. Looking at the schematic which is available (thanks, Steinigke!), we've got a traditional magnetic ballast arrangement. When you were replacing the lamps, did you inspect the socket for wear? These are maintenance items and should be replaced when they start looking gross. As a general rule, you never want to put your meter on the outputs of an igniter, they can hit some silly high voltages during strike that will exceed the ratings of your leads and meter. This is a moving light of the old school.

Futurelight phs 250 user manual