Oil Burner Cycles on and Off Every 10 Minutes for a Few Seconds

My regular oil burner (hydronic baseboard) cycles on an off every ~10 minutes even after the upstairs has just been warmed up. The combustion fan starts, oil ignites and runs for 2-3 sec's then, pow, the unit shuts down. The baro shakes. Burner is a Reillo, control is a Honeywell with min, max, and diff settings that were not touched from last year.

When I push up the temp on the thermostat upstairs, the circulator kicks in, burner starts and runs happy for several minutes like it should, then shuts down when temp is reached , this suggests it's not a oil supply issue.

What do you think is up?

loose wire somewhere? maybe adjust your settings 1 or 2 degrees maybe a bad spot in the adjustments....

I turned the differential knob a bit, See what happens.

sounds like the heat anticpater on the thermostat turn it up or set it to the amp draw of the controll the tt ties into if you've got zone valves turn it all the wayup longer run

The eye on the gun isn't always seeing the flame and shuts it down (it is there to prove the flame, shutdown prevents it from filling the combustion chamber with oil if it keeps running). Most have trap door on top of the burner, it may be what the ignition transformer is mounted on. Open the door and you will see a small cell with a few wires aimed at the burner's tip, clean it carefully with a soft, moist cloth and then re fire the burner.

eye is a good start, also if you can get to the injector nozzle, make sure there's no carbon build up on the end. Same thing happened to me and the service guy had to clean off the injector nozzle because the carbon buildup wasn't allowing proper atomization of the fuel, hence an improper flame was "sensed" and the unit would shut down.

Good point. The eye is a safety device and extremely sensitive to what it wants to see. To work properly the unit should be cleaned and serviced regularly and the burner nozzle replaced. A bad nozzle will eat a lot more fuel and they all go bad a little too quickly.

getting fuel oil to the nozzle? The tank isn't empty is it? Clean fuel filter?

Never mind, I just saw your line where its not an oil supply issue.

Usually if the eye doesn't see the flame, it will shutdown & lockout until you manually reset it.

Could just be short cycling, due to your house being warm from the coal .... which then makes the oil unit waaaay oversized for the house.

You could lower your high limit to stop the burner from running.

bad flowcheck ?
grab each loop pipe - all should be cold when no call for heat

if it were a issue with flame detection, the riello will lockout after trial when called to fire. it will retry once or twice if the flame drops out after it passes the trial period, so the issue is in the controls. like jim d and franco b write, likely the anticipator of a mechanical t-stat is set too low causing a zone valve to short-cycle - common problem with t-87 running taco zone valves. Also a problem with the new electronic 2-wire replacement for the t-87 which "robs" power from the t-t circuit, again plays hell with tacos. Airbound loops can do this since the boiler will bounce off high limit, but no heat will circulate. sorry for the extra noise... hope it helps.

one more idea - taco heads sometimes rock out of position causing a call to the boiler that acts like you describe. twist all of the heads clockwise to make sure they are properly seated...