Burner has to be reset every time

Looking for help with a Reillo oil burner on a Clyde boiler. Fires up OK and runs for an extended period, until the thermostat cuts it out I think. It wont restart again until you hit the reset button. I got a replacement controller box (secondhand) but still have the same problem.

Have you cleaned the photo cell and what colour smoke are you getting from flue

Which reset button do you have to press?

The red lockout button on the burner or the one for the thermostat normally located up by the adjustable dial?

How long is an extended period?

If you are saying its running for an extended period, then the photocell is probably not the issue.

Normally, you have 2 thermostats on a boiler, one for the adjustable one for the water temperature settings between 65-90 deg approx. and then the over temp one which is just above this.

If the adjustable stat is bust then then temp will go above the highest setpoint on the adjustable and trip the over temp stat, needing a reset. You then have a problem with your adjustable stat and it probably needs replacing. Happened to me before. They are about €25 I think and easy to replace.

Thank you for your suggestions
I checked the photo cell and it's clean. I have not noticed any colour in the fumes but cannot check at the moment as it's dark when I get home.

I have been using the reset button on the control box, the thermosat that I have has no reset button visible just a dail to set the temp. The temperature in the rads and tap does not appear to be exceptionally hot so I think it is cutting out at the correct temp. I removed the cover on the control box to see exactly what is happening. Initially it comes on OK and works until the thermostat cuts it out, the issue appears to be when it the temp has dropped and it attempts to restart, the blower (I think) comes on but when it tries to ignite it trips the reset.
You can reset if after a couple of minutes.

so you are saying it will start up the first time you ask it to when the system is cold but then when you have it on for a bit and the boiler/burner heats up, it won't start the next time?

there are really only a few things that should cause a lock out and the main contributor is the photocell. Sounds like thats ok as it works initially, but thats not to say I would rule it out.

Other items to consider are the motor/pump coupling could be slipping or the solenoid valve might be intermittent

Watch those bloody photocells, I spent a week trying to sort out a boiler/burner and if I had of spent the few quid on a new photocell on day one it would have taken a half hour. The cell was intermittingly faulty which was a pain to pinpoint.

Also have a look in the boiler itself to ensure the baffles have not become displaced. This can sometimes lead to smoke re-entering the chamber which would stop the first restart (it takes that extra fan time to clear the smoke)

my sis had a bad photocell in hers over xmas after the control box had been replaced and it was also intermittent.

I would change it first before looking anywhere else

Thanks, I will try that.
I will let you know how it goes

I replaced the photo cell last Thursday, ran fine until Saturday evening and then tripped out again. Once I reset it ran until Monday evening but now it's back to a single start and requiring a reset nearly every time. I am thinking that if the new cell temporarily improved it is it something to do with dirt accumulating on the cell but I checked and it looks perfectly clean
Any suggestions what I should check next

Clean the oil filter and check the line for kinks.

During the day what colour smoke are you getting from flue?

Also your electrodes, which are the two bars that meet over the nozzle, may need replacing. Check them carefully for any signs of breaks and/or reseat them in their socket. Also check the spacing at their ends above the nozzle. It may be that your burner can get up enough power from the transformer to fire the electrodes once but something happens then to stop it kicking off on restart. Difficult one to check that and rule it in or out.

Cleaned oil filter, some dirt in it but it has not solved the problem. I have checked the line for kinks and nothing visible. I took out the electrodes, no burning or cracks on them, cleaned them with sandpaper and put them back. Can anyone advise what the gap should be between them and it's position in relation to the nozzle. I reinstalled it and still have the same problem, firing first time but will not restart without a reset. I checked the fumes colour over the weekend and it is clear . Any idea's what I could check next

gaps typically about 6mm apart and about 5mm from the nozzle

sounds like the problem is occurring after it heats up, so I would think its a mechanical issue

When it doesn't restart, and you hit the reset button, will it start up immediately or do you have to wait until it cools down?

Solenoid/pump/motor maybe in that order next

I wonder is the air shutter getting stuck when the burner has run for some time. It might be worth watching the burner after the reset, once it has reached temp, then looks for a restart see does the air shutter door open cleanly. It only has to open an inch or so. In fact see does it close on shutdown having reached temp.

It restarts as soon as I hit the reset button
I have been checking the air shutter, it does not seem to move at all. It is open about an inch but anytime I check it, it is in the same position. I can move it manually. At what point should it move ? If it's not moving what would be the likely cause?

Latest update, still in trouble.
I have replaced the hydraulic ramp that operates the shutter. I discovered that the pipe that connects the oil supply to the ram was severed and had been sealed off so there has been no movement of the shutter for several years. I have also replaced this pipe. The shutter opens fully as soon as the burner ignites, but it does not close at all even after the the burner shuts down it remains fully open. I can manually close.
Should it close on shutdown and would it be a gradual closing?

the air shutter should close down when oil isn't being pumped into the burner. anyway this isn't the problem. in my experiance it is one of three things, 1 photocell 2 control box, or 3 injector (nossle). it's nearly always 1, but since you have changed this, that rules that out. you said you also changed control box. it would be worth pulling off control box and look for any damage/rust etc to connecters where the box meets the burner. I don't think it's the nossle but if you want to change it here is how. pull burner out of boiler. remove blast tube by loosening the two philips screws, a good tip is to put the screw driver in the screw head and give it a little tap with a hammer to jolt them and makes it much easier to screw out. now you'll find the nossle and electrodes, check the electrodes to see if they look ok. you remove the electrodes using philips screw, note position and distance from nossle as they will need to go back the same way. get 2 small adjustable spanners hold the stem with one and screw out the nossle with the other. this part is very important, when the nossle is out wipe it off and take to your local heating merchant as there are loads of different types. if the nossle is partly blocked it will cause lock out. Let me know how it goes, good luck!

I wonder is your oil pump acting up. Has the bypass screw being removed. If it is there it will have an allen key head. see here for details [broken link removed]
[broken link removed]

Is the boiler located in the house (or at least within the structure)?

Is the water pump operating when the burner switch trips?

Thank you all for the assistance. I think I have the air intake shutter working correctly now. I adjusted it so it opens about half way when the ignition happens, also its now closing slowly after the burner cuts out. But alas it has not solved the problem. I will tackle the nozzle next. I cannot see anything that is adjusted with an allen key, there is a blanking cover/nut on the side of the pump with a centre threaded inset that is adjustable, would this be the by pass valve, if so could it need adjustment ? The boiler house is part of the main structure , the water pump and burner have individual sockets which are contolled by the timer in the house. Th water pump continues to operate when the burner trips out . Thanks again to everyone for your help