The heater is about 20 years old. We checked it and weren't getting 24 volts for the gas valve. The ignitor control was replaced with a Robertshaw 780-910 Hot Surface Ignition Module and it worked fine. The next day, it wouldn't light again.

We reset the control by turning off the power and it worked perfectly. A few hours later, it wouldn't light up again. Over the next couple days, the same scenario. It won't light. I unplug the heater and plug it back in and it works until the heat goes off and tries to come back on.

What should we check? I noticed the control is supposed to have either a 4 or 7 second ignition trial time, but I don't know how to change it to a longer time or that this would help.

A few things to check is to make sure you have a good ground for the control and your gas valve. Make sure your flame sensor is clean. With some older systems when you put on a new control board the 24v transformer is not strong enough to give 24v it maybe around 18v or 19v at times giving you intermittent problems.

Thanks. We finally solved the problem. Changing the ignition control to go for 7 seconds instead of 4 before checking for ignition and having it retry 3 times solved it. Then my buddy thought to check the gas pressure. Sure enough it was very low, 2 lbs. Now it made sense that resetting and restarting the heater would work and not work later as the gas wasn't quite getting there to ignite in time. Adjusting the gas valve to increase the pressure seems to have solved the problem.