There are a bunch of these heaters sold under lots and lots of names.
This one in for repair is a Kende spark 30, 28kW, on wheels
There was a small fire that ruined the wiring and destroyed the photocell (LDR) Parts are readily available in the USA, but not in Europe at anything approaching a fair price. The PCB got toasted when the wiring shorted to chassis. The PCB is live chassis. There is just an on switch.
Very simple operation. The fan and ignitor run all the time via a triac. If no flickering is detected by the LDR (either the flame or ignitor) it shuts down in 2 seconds. To reset unplug for 10s.
The LDR choice doesn't seem critical so long as its change off resistance is enough keep the schmitt NAND from triggering. See the circuit for some figures. I had to replace the Q3 transistors (generic BC547) and the IC CD4093
