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

[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

 

[Chalked]

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.

 

[oilypig]

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

 

[lame plumber]

try a new photocell

 

[oilypig]

try a new photocell

Thanks

 

[jensda]

have you cleaned the filter on burner or just the line maybe coil as well

 

[lame plumber]

if the pump and fan are running ok continuously its unlikely to be capacitor/coil

 

[jensda]

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

 

[kimbo]

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

 

[Roger Welton]

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.

 

[Bunker]

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?

 

[kimbo]

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

 

[Bunker]

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

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.

 

[oilypig]

oops....filter on burner? where be that? it's a g5. Thanks

 

[oilypig]

Also if left an hour or so it relight and run again after a few cycles of not locking out as described originally.

 

[Bunker]

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.

 

[Roger Welton]

oops....filter on burner? where be that? it's a g5. Thanks

Under end cover of fuel pump.

 

[Bunker]

Also if left an hour or so it relight and run again after a few cycles of not locking out as described originally.

coil coil coil coil

 

[jensda]

most coils only start acting up when hot but check pump filter first and it costs you nothing

 

[Bunker]

most coils only start acting up when hot but check pump filter first and it costs you nothing

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.

 

[oilypig]

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.

 

[oilypig]

Oy ! just found this...
dont seem to be getting 50v on white wire from motor :-( is it saying its the motor?
http://www.rielloburners.co.uk/lumo...rtfaultfindingfor535seldrdbseriesburners2.pdf

 

[MarkOil]

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.

 

[jensda]

Oy ! just found this...
dont seem to be getting 50v on white wire from motor :-( is it saying its the motor?
http://www.rielloburners.co.uk/lumo...rtfaultfindingfor535seldrdbseriesburners2.pdf

are you checking this at terminal 7 on the control box I think its 7 correct me if incorrect

 

[oilypig]

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