I am working on a Laars LD400NL heater, low nox version with fan, of which there are very few out in the field. The problem is the heater will fire every time but shuts off after 2-3 seconds. I suspect the flame sensor, but not even Zodiac has the correct part number. They show the R0334300 which is a standard LD flame sensor integral to the burner. The LD400NL has a totally different burner and the flame sensor in this one was previously retrofitted with one that has the 45 deg bend in it. It appears a hole was drilled above the 2nd and 3rd burner to insert it.
When the heater shuts down, I am still getting 24V at the IND and TH terminals, gas pressure is around 7.5" and drops to 6" when valve opens. I am out of answers other than the flame sensor (also tried new R0480100 IGN Control) but I do not have a way of "jumping out" the flame sensor and I can't find a source for the correct flame sensor part number. Any help would be appreciated.