I am having issues with my hot water heater. I can get the pilot light lit and there is a nice healthy blue flame on both the pilot and the pilot generator. The problem is that the burners wont ignite. I have jumpered the TH to TH connections to get it to fire and I hear a clicking noise, but no flame. Before I run out and buy a ney Robert shaw millivolt gas valve I was wondering if there is some setting that I might be missing to try. The Heater is a Raypac Versa Heater O55B. The whole system is new to me.

Is the filter running with good flow? Is the gas valve in the ON position?
Is the thermostat set higher than water temp?
If Yes to all of these and it doesn`t fire when TH/TP - TH is jumped then most likely your gas valve is bad.

Other possibilities;

bad pilot generator not putting out enough voltage
short in the control circutry
clogged burner orifaces