oil burner lockout after 7 seconds

[dfoss]

My Mistral Oil boiler uses a Monoflame Minor 1 kero pressurejet burner with a Danfoss BHO11.1 control which is now obsolete. Recently while re-arranging some programmer connections and changing a very worn/dirty main power switch I think I have "spiked" the control box or photocell.

The mod I was working on is complete and checks out so is not the problem. The boiler starts correctly and fires almost immediately but goes on lockout at 7 seconds - after about 45 seconds I can reset the lockout and it will do the same again.

I suspected the photocell because that is supposed to come on at 7 seconds. but the 057H2020 is no longer available. I got a 057H7079 which is one of the ones listed for the later BHO70 series control box but with that fitted it fails in the same way.

When I put a multimeter on my photocell - the original 057H2020 - it reads about 89kohms under a bright light and around 2Mohms in the dark - is this about right or too high?

I am not sure that it is the photocell but as I believe my only other course of action is to get a conversion kit to the later BHO70.10 controller using an 057H7224 conversion kit - which is in total gonna cost around £100+ - is there a simple way to bypass the photocell temporarily to check if the control box is OK - in which case I can carry on scouring the net for a replacement for the old obsolete photocell.



Does anyone know what the difference between early and later photocells is?
I found a datasheet on the later Control box which says:-

" The photo current is measured with a direct
current ammeter in series with the photo unit (+
pole on terminal 12. Max. 5 kΩ internal resistance
in measuring instrument). With flame, photo current
must be at least 65 μA at 230 V.
With no flame, the measured photo current must
be max. 5 μA at 230 V."

- howeve if my multimeter is right and it is mains voltage on the photocell my old one at 89Kohms plus the meter's 5Kohm would only pass 2.4mA - the later one measures about 1.7Kohm which could pass around 34mA with another 5Kohms in series - much nearer what the datasheet suggests.

Any help gratefully received

dfoss
When you get to my age every day is a new experience

 

[outinthestix]

The cell see's the flame and allows the burner to continue by telling the c. box all is well. If no flame occurs the cell will tell the box to lockout. Sounds like you need more investigation as to why the burner is not lighting. First thing to check is have you got fuel in the tank ? Next ,is the fuel reaching the burner ? check by slackening the flexi hose where it connects to the fuel pump. Several things could be the problem including the cell or box but you need to determine the cause before spending on parts which are not needed.

 

[dfoss]

The cell see's the flame and allows the burner to continue by telling the c. box all is well. If no flame occurs-------

Flame DOES occur - it ignites fine - fuel is there and pump bled just to make sure - I can see the flame is well established and cuts dead when the controller should pull in the photocell at 7 seconds

 

[Burnerman]

I'm hoping someone will come on to this one, but I seem to remember that the BHO 11 uses a Danfoss LD photocell, but when using the superceded controller a Danfoss LDS photocell needs to be used with it.
Probably the best way - eventually - is to upgrade to a Satronic TF832.3 which comes with its own photocell.
It depends on how long you need to spend on it, I guess.
Sorry can't be any real help - I've done the conversion from BHO 11's but it was ages ago.
John

 

[dfoss]

Burnerman - do you think it sounds like the photocell? - or do failed control boxes also shut down this way?


I'll have a look at the satronic in the meantime - thanks

 

[outinthestix]

Sorry if i had the wrong end of the stick. It's when you stated the burner fires almost immediately that threw me. The burner pre purges with just the fan at first before it fires so i took it that you meant the motor and fan had started but after the pre purge period it locked out without igniting.
Anyway burnerman is right about the cells for different box's and also that the satronic is better bet. Stix.

 

[Burnerman]

Put it this way - I've had more photocell problems than control boxes.....your resistance readings sound ok but this doesn't really mean much.
The photocell is my guess, but I'm really sorry I can't be more specific. It could be worth bumping the topic up from time to time so others catch it.
John

 

[dfoss]

Actually I don't think there is any prepurge on this - it piles straight in and when it's lit once it fires almost immediately from then on till it's been turned off and goes cold. even now when I try it from cold it fires after about 2 seconds of fan.

Until it failed that is - now it cuts dead at 7 seconds

 

[Burnerman]

Thats way too soon - the purge should be for about 6 sec ideally. If you look inside the BHO there should be a diagram of its operating cycle, I think.
John

 

[dfoss]

Thats way too soon -

You'r right - I looked again at the start-of-cycle diagam and the oil valve should open also at 7 seconds - and in fact the lockout should not kick in for another 10 seconds - so why does it go lockout at 7 - does this tell you the control box is shot??

It always fired very fast - maybe the oil valve dribbled a little to support that very first fire

or maybe its been starting at the seven second point and locking out 5 seconds (ish) later in a pre-failure sort of condition and has finally failed properly

I am looking at the HPS website and they offer a kit to convert to a TF830 from a BHO11 - is that the one you meant - you mentioned a TF832.3 above

 

[Burnerman]

If the control box is working, a 7 sec delay is about right...it needs this time to purge fresh air through the flue. Then, ignition starts, followed by the oil valve control. The ignition stops, the photocell can see light so keeps the oil valve open.
These mechanical things were never that accurate time wise, but an immediate start sounds strange, if the thing is wired correctly!
On old systems there was no purge or air valve control so either the thing lit or it didn't..but I really cant remember what control that was. The pump was a Danfoss RSA pile.
Your burner shouldn't ignite too soon - after all, the oil isn't switched on immediately anyway. Check out the control circuit diagram again?
John

 

[dfoss]

If the control box is working, a 7 sec delay is about right...

I just crossed posts with you - see my edit of my last post - I have been looking at your satronic suggestion:-

"or maybe its been starting at the seven second point and locking out 5 seconds (ish) later in a pre-failure sort of condition and has finally failed properly

I am looking at the HPS website and they offer a kit to convert to a TF830 from a BHO11 - is that the one you meant - you mentioned a TF832.3 above"

 

[outinthestix]

The tf830 is the one to go for

 

[Burnerman]

I think if I were you that would be the route to take...but HPS are great to talk to and have very quick delivery.
Mind you, if this doesn't work I'll emigrate
John

 

[dfoss]

Thanks both - I will talk to HPS tomorrow - It's too bloody cold to mess any further with obsolete gear.

Good job I have this running in parallel with a stonkin' great woodburner or I would be the one emigrating - or divorced - or shot - it's -10degC ouside and has been for a week

Regards
dfoss