Sooty Oil Boiler

Our rental house has a Grant Outdoor combi oil boiler.

Report from the letting agent is that it's burning sooty.

My normal plumber that services it, can't get to it before Christmas.

So I'm going down tomorrow to have a look.

Now I can do basic stuff like bleeding the oil pipe, cleaning the baffles etc.

But what would cause it to burn sooty? Mixture grossly wrong? jet ********?

dont really know much about them, but incomplete combustion? lack of air flow? blocked filter?

There's no air filter.

Being an outdoor model, it just sucks air directly into the burner. No ballanced flue to get blocked.

I'd go for a worn out jet, the mix is unlikely to have altered

When we had an oil boiler we used to replace the jet every year

I'm sure there's an old one left behing from a previous service. I'll try swapping to that until I can get a new one and a proper service.

Well it shouldn't hurt

I service oil boilers as part of my remit.

Soot is caused by incorrect burner settings.

Generally too much oil and not enough air.

You will be hard pressed to set up the burner without a combustion analyser or at least a smoke pump.

If it has been serviced properly every year then the nozzle should be ok. If the nozzle is blocked due to low oil levels in the oil tank then your boiler would be starved of oil and would run lean.

The problem will probably be starvation of air. Check the flue outlet as sometimes people put bins etc. directly in front of the exit point and the burner is unable to remove the exhaust gases quickly enough.

You will also have to clean the combustion chamber and this is a filthy job even with the Little Henry. 

There are proprietor products on the market whereby you put the product inside the combustion chamber and fire the boiler which will remove all soot deposits. (I have never used them but if you search Google 'HWOS' you will find the product.

Hope this helps but let us know the outcome

I've just been down.

I changed the burner jet for the old one that was there.

the baffles were VERY sooty, all cleaned out now.

The best I can say it it's working but there is just a hint of visible soot in the exhaust.

That's the best I can do.  My plumber with all the kit (burner pressure gauge, flue gas analyser etc) is not available until the new year, same as us sparks, rushed off his feet at this time of year.

So it will have to carry on like that until the plumber gets there. At least they have heating and hot water.

If it is over pressure, what would cause the oil pressure to be too high? I would have thought as the oil pump wears, if anything, the pressure will drop?

One thing that may be relevant. Every year, without fail, the tenant lets the oil tank run dry. Gets the tank filled, then calls to say the boiler is not working.  I went down just a few weeks ago, to do my normal thing, bleed the air out of the oil pipe then it fires up and seemed to run fine. No soot then.

Could that have caused this problem?

Very rarely have I experienced any significant drop in oil pressure except when the oil pump is either broken or the drive shaft is worn.

A common problem is people letting the tank run dry/almost empty and then getting oil delivered. When the oil is delivered all the crap at the bottom of the tank is disturbed and if the boiler is working during this time then crap is sucked right through to the burner. If possible never have the boiler running during and shortly after a delivery of oil.

Sometimes when this happens the nozzle is partially blocked and rather than a fine mist being sprayed a full jet or a dribble of oil is produced and therefore  proper combustion cannot take place. 

Sometimes, if the tank level has gone low, as well as the normal bleeding it pays to stick an air line up the oil pipe at the boiler end and blow all the carp back into the now full tank. You lose very little and guarantees the line is nice and clean.