Sterling 40 lockout

[cwalters]

I have a Sterling 40 that locks out on start up when the boiler is cold. The burner fires and after 4/5 seconds it locks out. If you wait the prescribed time before pressing the reset it the fires and works as normal i.e. works away coming on and off with the boiler thermostat until the room thermostat turns it off. If the boiler is still hot it will fire up again when the room thermostat drops below the set temperature, but if the boiler has cooled down to much it locks out again. You then have to go through the sequence above again, and so on and so forth.

I changed the capacitor first, no change, so I changed the control box , no change. Oil delivery is fine and it burns clean just a nice heat haze out of the flue.
Any thoughts?

Carl

 

[Terrywookfit]

What is your co/2 and FGT ?

 

[Boilerman2]

What Type & output is the boiler that the Nu-way/Bentone Sterling burner is firing, Sterlings can be problematic depending on the version, can the Photoresistor see the flame ? it might be worth trying a new one as they are only a few quid

 

[cwalters]

I don’t have the means to test the co/2 or the FGT ? which I assume is the flue gas temperature. The boiler and burner are only 2 years old, its been cleaned out and a new nozzle fitted every year and has been operating fine until now. I’ll either have to get someone in or try and borrow the test equipment, if you think this might help diagnose the problem.

The boiler is a Thermasaver 5070 Boiler House standard oil boiler. I thought about replacing the photo resistor, but ruled it out as it worked fine after reset?

carl

 

[Boilerman2]

From your original fault Description , it sounds like the Photoresistor

 

[cwalters]

It turned out it was the Photoresister, thanks again Boilerman2. Replacement was not straight forward. I ordered a Photo Cell for the control box model Siemens LOA24.171B2B which I have. What arrived was a small black photo cell with long flyleads. When I took the old photo cell out it turned out to be a longer redie brown color photo cell with shorter flying leads. One it seems is a QRB1 and the other QRB1.B so it's worth checking which you have before ordering it will save you time in the long run.

Thanks again to everyone for their posts

carl

 

[Boilerman2]

The sterling is fitted with a long cell (that tells you something!) but they should work with a short one , but at least you have sorted it, well done you!!