Oil boiler fault

[Cliff top]

I know this isn't really a forum for central heating faults, but I think its the best place to find someone with the experience I need.
Any thoughts welcome.


For the last year our oil CH has sat idle as we also use an Aarrow wood stove/boiler & Navitron thermal store piped into the same system and controlled by 3 way valves. (Its an Old Myson oil boiler block with newer Bentone sterling burner fitted) When oil was last used in Feb/Mar it didn't seem to be running as effective for heat output but would run continuously . Now when we fire the oil boiler up, to take the chill of the house before the fire is lit, it is cycling the oil feed on/off. The flue/boiler don't get anywhere near as hot as they should. Air fan is running constantly as it should, the burner will then cut in for perhaps 15 secs then shut off for 5 secs then repeat. The satronic TF830 module isn't going to lockout but is obviously detecting some fault condition....but what?

The oil pump pressure and airflow hadn't been altered although after marking the orig positions and experimenting with increased/decreased flows for both didn't alter the cycling but did change the burner sound and produced black instead of white smoke/vapour at one point. Oil flow is good, and the airways/flue are clear etc.

I haven't stripped down the burner nozzle etc but it does look clean. One of the retarder plates in the boiler had fallen into the bottom, I have now cleaned out the interior and refitted the plates correctly.
LAst week when the heating was left for 1/2hr cycling on/off the Danfoss EBI ignition unit failed with a melted side/burning smell. Replaced the module and the cycling is still there.

Is the cycling causing extra workload for the ignition unit and likely to have caused that to fail? or is this just a coincidence? Does the ignition spark continuously in normal use or just initially to get ignition?

The photocell looks ok, but if faulty would that cause this symptom?

There is precious little technical around on the net for Bentone burners, the fault finding I did find re: cycling, suggests an airflow/burner mix problem, so just wanted to get the benefit of anyones experience before stripping the burner nozzle etc down.

Thanks for any suggestions
Cliff

[Alan]

Hello Cliff

Sounds like the flame scanner cant see enough of the flame.
This causes the ignition transformer to keep cycling on / off.

Normally caused by the flame swirl plate being in the smallest diameter of the blast tube. Hence the cell is trying to look though the slots of the swirl plate only.


If you pull out the flame scanner quickly while its alight and shine a torch on it.
( If it's a light sensitive cell And not a Ultraviolet cell )
It will keep on burning.
Now look down the hole where the scanner should be located to get a view of what the cell is looking at. If you cant see a 360 Deg flame image around the swirl plate it needs moving slightly.

If you move the swirl plate back towards the burner front. ( away from the boiler )
The cell will be looking through the swirl plate and around the outside.

If it looks good the cell could be low in sensitivity and just needs changing

Regards

Alan

[renewablejohn]

Clifftop

 Not an expert but on our nursery we had several oil burners and with those problems the first thing I would replace would be the photocell. If I still had problems then we would replace the whole burner unit as we could not afford the loss of heating on a frosty night.

[Cliff top]

cheers chaps for the replies.

Alan,  I've just checked the photocell operation with some odd results, and then found out it probably has to be flickering infra red the sensor is looking at so my low energy inspection light won't do it!
Its just a photocell, not the IRD or UV sensors that Satronic also show, so I suppose it perhaps should work just with a normal light not IR flicker.
I've looked up The Satronic TF830 controller sequence of operation. It has a 20s purge and 5 sec trip mode.- just what I'm getting.
It may be as you suggest the sensor thats not reading somehow. Looking down the tube it looks bright enough and I've looked into the boiler chamber and tweaked the burner for best combustion, no difference.
I'll risk getting a photocell to try.
cheers
Cliff

[Justme]

Check your oil filters as well as a slightly reduced flow can have strange effects. Ours would go out if the wind blew in the wrong direction so the enginer removed the ballenced air intake. That sorted it but I was not happy. In the end I found the slightly blocked pre filter & after cleaning it it worked perfectly. They did say they checked the flow as well.

Justme

[pottsiwebber]

I've been nursing a 28 year old oil boiler along for the last 5 years and found this forum very good http://www.diynot.com/forums/viewforum.php?f=7&sid=1c63fb4a963f1d9014a86098f6509361

Normally if the control unit is detecting a fault it requires a manual reset. It almost sounds as if the thermostat is shutting the boiler down then asking it to run again.

I have had some odd faults caused by poor combustion one of which turned out to be a faulty solenoid on the oil pump allowing fuel into the burner before it should, but this results in a sort of stuttering / pulsing sound on shutdown and oil leaking into the burner when its shut sown neither of which you mention. The nozzles are also very delicate I wrecked one just by wiping it with a cloth to clean it resulting in noisy dirty operation until I changed it.

I still cant help thinking if a photocell did not detect a flame it should lock the boiler out. And yes if its a photo cell a sufficiently powerful torch should make it operate. If you have a multimeter and the inclination try and find out what resistance it should be in operation  and check it.

Good luck and try the forum I suggested there's a very helpful oil boiler expert there.

[Alan]

Quote “ I still cant help thinking if a photocell did not detect a flame it should lock the boiler out. “


There are various ways to control an oil boiler.

Satronic using a TF830 do it this way.

Flame failure during operation

The flame failure will be detected by the GZ or MZ photo resistor

Fuel supply will cut off ( terminal 5 )

Ignition circuit ( Terminal 3 ) is energised

The control box reverts to a normal start up, to safely relight the burner.

If the flame is re-established and detected the control eventually returns to the run position.

If the flame is not established or detected the control box goes to lockout.

On gas this type of operation is not allowed as a minimum of five air volume changes are required from the air fan inlet to the top of the flue system before any ignition source is operated.

Your system is working correctly and the cell is not seeing the flame sufficiently.

Regards

Alan

[Cliff top]

cheers again

Filters etc are ok. as are the themostats/couples.

Playing with the torch did change the operation slightly, so seems the most likely,but still waiting for the new sensor to try. The oil ignition/shutoff is instant in each respect, no stuttering so I think its running ok but for this control.

Did find the DIYNOT site too...quite useful.

cheers Cliff

[pottsiwebber]

Fair play Alan I'm only going by my old Danfoss control box. I noticed from your earlier post you obviously have a lot of knowledge regarding burner operation. Just adding my thoughts.

[Cliff top]

Wasn't the sensor   symptom just the same

further checks.. ignition spark runs for ~10secs then stops.. boiler continues another~10secs then solenoid clicks/ shuts down for 5 secs. ignition comes back on a few secs before burner comes on again.
There was plenty of oil running freely when I bled the pipework upon initial reassembly. Air fan healthy and not blocked etc.

I'll risk inspecting/cleaning the nozzle area next.

[lightfoot]

Hi Cliff,

I've just spotted your post and it's a bit of a long shot, but I thought I would mention it all the same....Last year, just as the heating season was upon us, a mate of mine phoned me up one night, looking for some advice on why his oil boiler kept locking out.  Anyway to cut a long story short - after getting him to check a few things and going through a bit of a over-the-phone diagnosis, it was discovered that there was no, or very little water in the system/boiler - causing the boiler to fire briefly before locking out.  Well according to my mate, he had a leak repaired by a local Plumber - on one of the DHW cylinder connections and the cylinder was temporarily removed to gain access etc...but apparently the Plumber was in a bit of a hurry (maybe too many call outs!) and had forgot to refill the primary circuit, as he had left the ball-valve in the F&E tank tied up...needless to say my mate released the ball-valve, filled and vented the system and away if fired.

As I say, it's probably not what's causing your problem, but sometimes you have to think a bit sideways....it's been a while since I've had much to do with oil boilers on a day to day basis, but I will have a bit of a head scratch and see if I can think of anything else that you haven't already covered 


Good luck and I hope you get to the bottom of it all.

Lightfoot.

[pottsiwebber]

Re-reading Alan's last post I think he is saying the controller will try to re-establish a flame if it loses the flame during normal running but will only try this once? If it re-establishes the flame it will return to run but if it doesn't see the flame it will then go to lockout? Feel free to correct me Alan.

I think I'm right in saying your boiler never gets to normal running but keeps starting and stopping without locking out. If so its not trying to re-establish the flame but switching it on and off possibly before reaching normal running.

If I read Alan's last post correctly I was right the first time around and if your boiler was stopping because it doesn't see the flame it would lock out after the second attempt otherwise you could potentially end up with a boiler full of unburnt fuel if for example the ignition was failing completely.

If it were me I would still make sure the controller is being asked to run continuously i.e. no thermostats in rooms or in the boiler telling it to stop. If it is then your controller could be caputski.

[Alan]

With a descent energy gobbling tungsten torch.

If you pull the cell out quick enough while it is alight and shine torch on cell.
It should keep alight. ( oil valve remains open and ignition transformer stays off )

If you pull it out a bit slow.
Oil valve closes.
Ignition transformer on.
Oil valve open.
If alight
Turn on torch.

Flame should stop on and be stable.

If the oil valve is clicking / de-energised there is a TF830 fault.

The timer is very crude with a Bi metal strip and contacts.

A Bash on the concrete some times helps.

Will have a look in the sheds in the morning, if I have got one will put in post.

Most of my stuff is bigger and gas but will have a look

Regards

Alan

[Cliff top]

Cheers again for the support.

Lightfoot... The boiler casing is ok, full of water, both stats ok etc.  The pump runs and the flow is ok as the pipework starts to get warm, just slowly due to the cycling. The system is also shared with the log stove/boiler which is working just fine.  I know what you mean...think outside the box eh?

Alan...  The plot deepens   Pulling the sensor out/shining a tungsten light doesnt cut off/change the operation significantly. 
The controller looks ok but there were a couple of things I wanted to look at,  since there was a little condensation inside so I dried it out. Upon refitting the fault actually seems to have gone worse... The flame fired up for just a couple of seconds before extinguishing...no apparent solenoid operation if I remember and more of a whistling/squealing noise from the fan/oil pump for the few seconds before it then goes to lockout.
Looking at the controller there was a slight suplhating around a couple of connections. Anyway, I have removed the cover,  dried/cleaned it thoroughly and at the same time cleaned each of the contacts with a strip of paper, so all looks ok now.  No difference on refitting. 
In case there was no oil, I tested this morning by removing the bleed plug...plenty of oil flow.so 
Have brought entire burner to work today and will strip it- (when I can remove the rusted allen bolts) in case there is a blockage where just a limited amount of oil gets through, eg enough to burn for 10 secs.
Is it possible the solenoid is only tripped momentarily by the controller, allowing a glug of oil? seems doubtful as it presumably requires oil pressure to spray oil out rather than relying on venturi suction.

[Cliff top]

Just found whilst stripping down-  the blue N wire back from the oil solenoid is loose in the bottom of the terminal block behind the controller. This explains the reason for the fault getting worse! oil pump pressure increases and whistles?

Whether this could be the main fault too....