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diesel heater cuts out


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Last year I bought a big steam cleaner, a WAP C900 from 1983. The heater uses a diesel burner. Used it a couple of times and it did a a good job (though a bit noisy and smoking). Earlier this year, I noticed the burner wouldn't light. Seemed to be a lack of diesel. So I started by cleaning the filter and nozzle and checking the diesel solenoid valve. Afterwards I did get a good spray of diesel, but no ignition. So I replaced the nozzle, thinking the spray pattern wasn't good. Made no difference. In hindsight, the setting for the electrodes was probably way off at that point, because I didn't pay attention when I replaced the nozzle. Fitted new electrodes as well, just to be sure. I always get a good spark, but the diesel spray doesn't ignite properly. I can usually get it to fire, then it cuts out again to light up again after a few seconds. I started with the electrodes set as per spec (as far as I know, not much documentation to be found), then moved the tips and while this has some effect, I can't get it to burn reliably. A few weeks ago, I thought I had it fixed, as it ran OK for about 15 minutes and the smoke darkened and then cleared. But last week it was back to pulsating on-off, and not able to get any heat into the water. I tried adjusting the diesel pump pressure and fitted a smaller nozzle, because less pressure seemed to give a more constant flame. At the moment, it's just usable, I get enough heat to make cleaning oily bits a lot easier, but it's not exactly steam. And it comes with a lot of smoke, white greyish, indicating unburned diesel.      

This should be a simple system, no electronic controls or safeties. Just air (fan is spinning and gives good airflow), diesel (I can see the spray in between firing) and spark (never a problem). But even when it fires up, it cuts out again. Never thought it could be so hard to get diesel to burn... Any pointers greatly appreciated. I'm sure it's something simple, but it's kept me off work for far too long already...


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