Danfoss BFP 21L3 oil pump - occasional failure.

[Willower]

I have a very old (40 years?) Worcester Danesmoor 15/20 boiler which has a Selectos burner. The burner was retrofitted with a Danfoss BFP 21L3 pump before my time with it. I have replaced most of the other things over the past few years.

What is happening now is that the boiler generally starts up OK and will run for periods of more than a day in some cases. More often than not it will fail after about 1 hour and lock out the controller.

I have watched it as it fails, and the process is that the flame fails but everything else appears OK until the photocell detects the failure and closes things down. Sometimes it picks up again before the lockout.

After the lockout period it always, so far, starts successfully.

It seems obvious that it is a fuel supply glitch, but I've tried bleeding everything in sight up to the filter on the pump. Is there some magic sequence which needs to be followed?

It could be the drive to the pump, which has been botched in the past, but I would expect a more definite failure in this case. These symptoms have been going on for two weeks or so.

Any thoughts would be welcome.

 

[Burnerman]

You've probably read elsewhere in the forum that the big failure part of the BFP range of pumps is the solenoid coil.....
The BFP 21 has a bleed nipple on the top - if need be, open it a fraction when the burner is running and any air will be purged out.
John

 

[Tipper]

As burnerman says I would replace the oil solenoid coil, but I would also get myself a spare plastic pump to motor coupling thingy and a new flame sensor/photocell. All cheap items in comparison to emergency call outs!

Change all three and see how it goes. Keep the old ones for spares and get your friendly local engineer to service it ready for the winter. It's good to have a new nozzle, have the oil pressure checked and a combustion test and burner adjustment made before the weather gets really cold.

 

[MANDATE]

I once had a similar problem on my selectos burner, although at the time my pump did not have solenoid. I did find slight improvement after a delivery of oil.
Got to thinking pump not up to much pulling power when tank low on oil.
Fitted a pressure gauge and found lowish pressure which could not be adjusted to the required 100psi.
Concluded pump was worn after some 15years and fitted replacement.
Sunstrand replaced with Suntec AS47C7451.
Problem cured.
So my thoughts in addition to solenoid. Age of pump? worth checking pressure to nozzle. Tank oil level below or above level of pump.

Once had drive pin of pump gears snap on Sunstrand, but could never come up with reasonable explanation of how it happened.

 

[Willower]

Thankyou for the interest. I think that for the moment I shall have to wait until the problem becomes more reproducible. It is the fact that it runs for an hour or more which makes things difficult to diagnose and at the same time relatively simple to live with.

FYI, while the solenoid valve may often be a problem, this burner/pump has two such valves. One is integral with the pump, near the filter, the other is on a separate brass casting on the high pressure feed from the pump. I assume this must be a left over from a previous pump version, it has always seemed somewhat redundant..

Thanks again

 

[Boilerman2]

Is the flame Stable on th flame ring?
The D.42, whilst a luvverly old burner, has a tendency for "flame lift off"
which can be detected by sound (sounds a bit uneven, and looking through the blue sight glass, the flame flickers - this results in the PE cell not seeing the flame properly and LOCKOUT.....just a thought!

 

[Willower]

Boilerman2

That sounds plausible. Normally when I look the flame is obvious - but I remember looking once a few days ago and thinking that there was not much sign of the flame - although I could hear it of course.

Is there a solution? - perhaps reducing the airflow, a new injector, or something?

Regards

 

[MANDATE]

This might be of interest.
http://en.wikipedia.org/wiki/Flame_lift-off

I also recall having to set front of nozzle 6mm back from flame ring and front of electrodes in line with front of nozzle, although the spark takes place about 5mm further back due to the shape of the electrode ends

 

[Boilerman2]

To fully answer your last question i will need more info from your burner
look at the "Selectos" label and post the burner make as it appears
i.e. D42/A or D42 T.34 etc etc, this will tell me which combustion head is fitted to your burner

 

[Willower]

Boilerman2, Mandate

Thanks for the help.

The burner is a Selectos D42/T26.

I'm going to get a replacement photocell to see if that doea anything - at least it's a relatively cheap step to take.

 

[Willower]

Just a final note - I hope it is working now.

I tried a new solenoid on the pump, having removed the apparently redundant valve. The result of this was to show that the valve on the pump was jammed open, and presumably the extra valve was to "cure" this. The failure I had was in the second valve which presumably had a solenoid problem as the unit got hot

Given the known age of the pump, and the relatively small price of a replacement pump, I fitted a new unit ( ± £30 for a valve stem vs ± £50 for a pump and solenoid). I also replaced the plastic drive train. It all seems to be working now. - and I have a spare solenoid for next time.

Thanks again for the interest