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Oil boiler flame cuts out but no lock out and cycles continuously

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oilypig

Hi
Any ideas please?
The boiler runs fine for 20 minutes approx then flame cuts out the oil pump continues to run The flame relights for a couple of seconds and cuts out again. This then carries on indefinitely, pump running all the time flame relighting and going out every few seconds.
It does this in or out of boiler chamber.
I do not have to press reset to get as the pump does not stop running.
I have emptied/cleaned the filter/water trap.
I have bled the pump.
There is about 6" of fuel in tank.
It is an old system been working for years.
I have measured resistance of flame sensor with light on and off and it seems to work ok going from high to low resistance when light shined on it. Also checked nothing blocking detector from seeing flame.
It is a Grant euroflame 50/90
Thanks
 
Do you have a flue gas analyser and are you oftec registered. If not you shouldn't be fiddling.

But 6 inch of fuel, barely covers the outlet.
 
Thanks
Yes but its home in England.
Sorry 6 inch above outlet from tank, but not a great deal of 'head' but it's been run dry before with no problem.
cheers
 
if the pump and fan are running ok continuously its unlikely to be capacitor/coil
 
would agree lame plumber but had a 3gb with similar problem last year and it was a faulty coil usually coils fail after a certain run time when hot but not this one for some funny reason def not a capacitor I would think as well as there is no lock out it does sound like fuel starvation or over airing
 
Could be faulty oil pump that when gets hor loses pressure. Check with gauge. If it was photocell I would expect it to go to lockout. I would then go for control box. There could be more than one fault
 
If photocell gives a false light reading then burner runs continually and won't lock out, as lp says photocell first, if ok then control box.
 
OP says he's tested pcell but that is the obvious choice.
Is it the early model with the Mecron or the later with the RDB Burner?
 
According to post the burner doesnt run indefinetly without lighting otherwise as roger says the cell is seing a false light. The burner us firing and going out repeatedly.
Sounds like a g5 burner or g3 on these
 
kimbo said:
According to post the burner doesnt run indefinetly without lighting otherwise as roger says the cell is seing a false light. The burner us firing and going out repeatedly.
Sounds like a g5 burner or g3 on these
Click to expand...
Yeah, so if its seeing a false light, the ignition wont come on atall? COuld be worth having the pcell off and wire brushing the contacts but Im also liking the sound of the coil: runs for 20 mins before cutting out? Then repeatedly? Could be too weak to hold solenoid open.
 
Also if left an hour or so it relight and run again after a few cycles of not locking out as described originally.
 
Just a thought - when you cleaned your filter bowl, was there much water in there? and how did the filter look - that could give you an indication as to the condition of the pump filter. Personally Id leave that til last resort, the pumps dont like being opened and closed again..
There's lots of stuff an engineer could try with the right kit but most of it we cant really talk you through.
 
jensda said:
most coils only start acting up when hot but check pump filter first and it costs you nothing
Click to expand...

Exactly. Op states runs ok for 20 mins then starts playing up. He also says later that if left for an hour, it's ok for a bit, ie coil cools down.
 
ok thanks muchly for all suggestions.
I have now cleaned filter in pump and checked free flow of oil into it. Not much crud at all and certainly not blocked.
Ran it with pc unplugged as a double check and it just locked out as expected.
Will try changing coil as that seems consensus? Failing that the control unit maybe?
Will post result.
 
Check your meter is on AC and that your tester is fully in to make the connection, because poking it in the back of them plugs can be a tad tight. But yeah if your not getting the voltage, then to me that seems like the problem.
 
Yes its 7 and thats counting from the left with 2 blanks included
I do have the voltage from pump so going for coil for def.
cheers will report
ta muchly
 
I'm replacing the solenoid on Friday.
Will report back then thanks.
 
Might well be solenoid in this case, but Riello oil pumps cause same symptom sometimes. Seen them running for a many minutes from cold start & then "slipping" causing the burner to try to ignite again & again in little bursts.
 
kimbo said:
Could be faulty oil pump that when gets hor loses pressure. Check with gauge. If it was photocell I would expect it to go to lockout. I would then go for control box. There could be more than one fault
Click to expand...
As said earlier check with gauge
 
Hi all,
Have now replaced coil.......no change, runs for 20 mins from cold and then turns off and when restarts just cycles round flame starting up and cutting out after a few seconds, but no lock out.
Same inside chamber or out incidentally.
So.....Oil pressure from pump or photocell(which appears to work on a simple ohms test) or control box?
Thanks again for all the help.
 
oilypig said:
Hi all,
Have now replaced coil.......no change, runs for 20 mins from cold and then turns off and when restarts just cycles round flame starting up and cutting out after a few seconds, but no lock out.
Same inside chamber or out incidentally.
So.....Oil pressure from pump or photocell(which appears to work on a simple ohms test) or control box?
Thanks again for all the help.
Click to expand...

You would have been better with a photocell & control box with you & tried them starting with the photocell, as you only need 20min to wait. Either of those parts can do same symptom but personally I always am wary of Riello oil pump. Riello solenoids are rarely faulty. If you are confident to open the oil pump you could check to see if any serious wear inside it. You would need a new oil pump with you if it all goes wrong though! :smile: Here's my way of checking the pumps if you are interested, - Remove the oil pump cover with burner in normal vertical position & take filter off. Often the O ring seal is stuck to the pump body & you then need to push it into the groove on the cover. Now turn the burner so the pump is horizontal (this will stop the gears falling out) & remove 2 of the 3 screws on the gear cover. Slacken the 3rd screw & turn the cover to the side & take a look at the pin from the shaft to the gearing. If it is cut into the gear then it might be slipping. Don't overtighten the gear cover screws if pump is okay.
 
Last edited:
Ok
I have now tried shorting out the photocell on a switch.
So wait for it fire up turn switch short on.
Runs fine.
System turns boiler of after everything piping hot.
I open short.
When system calls for boiler again it fires up I throw switch flames stays on.
I am obviously doing this only in attendance as I'm overiding the safety device.
So thinks me , it has to be the photocell!
And amazingly, yes I can get one in this god forsaken place.
So bang it in and voila......................................no change!!!!! (Yes I have checked that there is nothing stopping photocell seeing flame)
I reckon I have proved pump and motor and pressure and everything like that?
Must be the control box right?
Please tell me if I'm wrong.... Thankyou my patient friends. :-/
 
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