OT: Oil burner control

Definitely not PLC related, but maybe someone can offer insights.

The burner controller on my oil furnace is a Carlin model 40200-02 which appears to be an obsolete model. The igniter is working properly and there is a good flame. The burner is supposed to start and stop based on the water temperature (aquastat). Once started it will run for 5 -10 minutes until the water temperature reaches the cutout point. The problem is that it doesn't relight when the water temperature drops below the setpoint. I have to hit the reset button on the controller to get it to restart.

I disconnected the wires to the aquastat, connected an ohmmeter and verified that the aquastat switch is opening and closing. I connected a jumper to the aquastat connection terminals on the controller and even that doesn't make it start.

Anybody familiar with the unit who can offer any additional troubleshooting suggestions? I'm planning to call the service tech tomorrow when I don't have to pay weekend rate for a service call.

If you have to hit the reset button, it appears it's locking itself out on an overtemp fault. If it's not going overtemp then you probably have a faulty controller.
Maybe try lowering the controller temperature a little [if your process will allow it] & try that.

I dont know that brand but as Secpcb has stated its being locked out, there should also be flow switches and maybe level, sounds like one of them is bouncing and locking it out

It turned out to be the flame sensor failed in the on state. Since the controller thought the flame was already on it wouldn't go into the startup sequence. Hitting the reset forced it into the startup and it stayed on because the flame sensor was satisfied.
The technician figured it out by installing a new controller which has a digital display and troubleshooting codes. He said he'd seen plenty of flame sensors fail to detect flame, but this was the first one he'd seen fail in the on state.

I have seen them fail 'on' before. Usually through heat damage.
But I had the benefit of seeing flame strength leds that were lit when I knew there was no flame.
But all controllers check 'no flame' signal before commencing the ignition cycle.

Steve Bailey said:

It turned out to be the flame sensor failed in the on state. Since the controller thought the flame was already on it wouldn't go into the startup sequence. Hitting the reset forced it into the startup and it stayed on because the flame sensor was satisfied.
The technician figured it out by installing a new controller which has a digital display and troubleshooting codes. He said he'd seen plenty of flame sensors fail to detect flame, but this was the first one he'd seen fail in the on state.

Click to expand...

It is not unusual for UV Flame sensors fail ON. This is why they make self-check UV scanners.

Don't know what this one was, this is just general information.