Having trouble diagnosing a unit heater short cycling. I have exausted my resources on this one as I've done almost everything possible aside from replacing the gas valve-I've tested/replaced flame sensor (.8 microamps) tested/replaced pressure switch (spec=.86/measured >.92) tested high limit @ fault (remains closed) and above all, replaced the control board-which didn't solve anything. So I'm currently at loss. The unit is located in a filthy fab shop, which I think plays a part. Also, last summer, a gas leak was discovered and a leak test was performed. Based on my diagnosis, I'm wondering if the gas valve is at fault here. When I tested the gas valve, the pressure was almost spot on and power (24v) was consistent until the fault. Could it be that when the leak test was performed, it blew out the pressure reg and/or the heater gas valve? Assuming the cock valve wasn't turned off. BTW there is a another unit heater in this facility that is exhibiting the same symptoms. Two other unit heaters working fine-now and one I found with the manual valve off. Any ideas?
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