I had my central heating oil boiler serviced last year, it had a
bearing replaced in the motor.

Since then it seems to burning a 'rich mixure', i.e. there is a very
obvious kerosene smell from the exhaust. And the oil fill seems to be
used quicker.

There is a mixture screw/valve in the side but when I tried to adjust
it the burner stops and refuses to start again of its own accord
unless I increase the mixture.

Is it the quantity of fuel or the lack of air? Or am I completely on
the wrong track.

I can't remember the burner model number but if it helps I can look it
up to-night.

regards

MJW

"Michael Walsh" wrote in message
om...
I had my central heating oil boiler serviced last year, it had a
bearing replaced in the motor.

Since then it seems to burning a 'rich mixure', i.e. there is a very
obvious kerosene smell from the exhaust. And the oil fill seems to be
used quicker.

The smell is not forced to be due to a rich mixture. Unlikely though it
sounds a weak mixture also creates smell in the exhaust gases. There is a
fairly narrow band in which the mixture is "correct". In this band the
efficiency peaks, outside it the efficiency falls off fairly rapidly. Rich
mixtures invariably leads to soot formation which manifests itself as
visible smoke and soot deposits around the flue discharge. Weak mixtures
smell sour and the excess air causes the heat produced to be swept through
the boiler and out of the flue too fast to be absorbed by the heat
exchanger. In both non-ideal cases the fuel usage goes up.

There is a mixture screw/valve in the side but when I tried to adjust
it the burner stops and refuses to start again of its own accord
unless I increase the mixture.

Depending on the screw it might be the pump pressure adjuster. Is it on the
burner casting or on the oil pump?


Is it the quantity of fuel or the lack of air? Or am I completely on
the wrong track.

See above. It may be pertinent that the burner motor had a new bearing
fitted as this would involve removal of the fan and cleaning off of the
blades during reassembly. This gives fan delivery performance improvement
and weaker mixture results.


I can't remember the burner model number but if it helps I can look it
up to-night.

It would be a help, together with the make and model of the boiler

Hi

Thanks for the info. I will have a look at the Flue to-night for soot.

Your suggestion about a weak mixture might well be right, The fan was
wire-brushed and alot of muck was removed from it so it may well be
supplying more air at this stage.

The valve I talked about is part of the 'pump' which is mounted on the
end of the motor. The oil feed line comes in one side and there are
two hex-nuts on it. One of them is used to bleed the pump when I run
out of oil and I have an air lock. The other hex nut (about 10-12mm in
size) has a screw in its centre about 4mm with a screwdriver slot in
it. I took it out once and there is a small spring inside it so I
guess it is probably the oil pressure adjuster.

What should I do to fix a meak mixture? I will get the make and model
of the boiler also when I get home and post it later on to-night, I
think it is a Riello but I will check to make sure.

regards

MJW

"John" wrote in message ...
"Michael Walsh" wrote in message
om...
I had my central heating oil boiler serviced last year, it had a
bearing replaced in the motor.

Since then it seems to burning a 'rich mixure', i.e. there is a very
obvious kerosene smell from the exhaust. And the oil fill seems to be
used quicker.

The smell is not forced to be due to a rich mixture. Unlikely though it
sounds a weak mixture also creates smell in the exhaust gases. There is a
fairly narrow band in which the mixture is "correct". In this band the
efficiency peaks, outside it the efficiency falls off fairly rapidly. Rich
mixtures invariably leads to soot formation which manifests itself as
visible smoke and soot deposits around the flue discharge. Weak mixtures
smell sour and the excess air causes the heat produced to be swept through
the boiler and out of the flue too fast to be absorbed by the heat
exchanger. In both non-ideal cases the fuel usage goes up.

There is a mixture screw/valve in the side but when I tried to adjust
it the burner stops and refuses to start again of its own accord
unless I increase the mixture.

Depending on the screw it might be the pump pressure adjuster. Is it on the
burner casting or on the oil pump?


Is it the quantity of fuel or the lack of air? Or am I completely on
the wrong track.

See above. It may be pertinent that the burner motor had a new bearing
fitted as this would involve removal of the fan and cleaning off of the
blades during reassembly. This gives fan delivery performance improvement
and weaker mixture results.


I can't remember the burner model number but if it helps I can look it
up to-night.

It would be a help, together with the make and model of the boiler

"Michael Walsh" wrote in message
m...
Hi

Thanks for the info. I will have a look at the Flue to-night for soot.

Your suggestion about a weak mixture might well be right, The fan was
wire-brushed and alot of muck was removed from it so it may well be
supplying more air at this stage.

The valve I talked about is part of the 'pump' which is mounted on the
end of the motor. The oil feed line comes in one side and there are
two hex-nuts on it. One of them is used to bleed the pump when I run
out of oil and I have an air lock. The other hex nut (about 10-12mm in
size) has a screw in its centre about 4mm with a screwdriver slot in
it. I took it out once and there is a small spring inside it so I
guess it is probably the oil pressure adjuster.

What should I do to fix a meak mixture? I will get the make and model
of the boiler also when I get home and post it later on to-night, I
think it is a Riello but I will check to make sure.

Step 1

Get installation/ maintenance manual from boiler manufacturer this will tell you
what oil pressure to set, as well as co2 and flue gas temperature (and smoke) .

Step 2

Acquire oil pressure gauge from HRPC (or other supplier) Cost about £35 with
manifold. 0-300psi is likely OK.

Step 3

Check what Jet you have in boiler and change if more than 1 year old. Cost £7 or
so. (HRPC)
Quite often boilers accept a range of Jets to provide different heat outputs

Step 4

Install above. Now the problem is to set the air supply correctly. You need to
find the adjustment for the air shutter.

I suggest that you ask the boiler manufacturer if they can advise you on the air
setting for the particular jet you are using (if not mentioned in installation
manual)

In an ideal world you should measure the % Oxygen in flue Gas, calculate the co2
% and compare to figures in manual. The problem is that an 02 meter will cost
£200 + They also use sensors which have to be replaced every 2 years. You can
use a chemical kit - similar initial cost.

You should also check the flue gas temperature. A thermocouple & meter to
measure the flue gas temperature can be had for less than £60. Alternatively
some electrical multimeters come with this facility.

It could be that if you start with the air shutter fully open and have a low
temperature reading, you could progressively close the shutter until you get the
correct temperature reading and thereby achieve a reasonably efficient set-up,
but I have not tried this.

You can get equipment for checking the smoke for about £60.


Michael Chare

"Michael Walsh" wrote in message
m...
Hi

Thanks for the info. I will have a look at the Flue to-night for soot.

Your suggestion about a weak mixture might well be right, The fan was
wire-brushed and alot of muck was removed from it so it may well be
supplying more air at this stage.

The valve I talked about is part of the 'pump' which is mounted on the
end of the motor. The oil feed line comes in one side and there are
two hex-nuts on it. One of them is used to bleed the pump when I run
out of oil and I have an air lock. The other hex nut (about 10-12mm in
size) has a screw in its centre about 4mm with a screwdriver slot in
it. I took it out once and there is a small spring inside it so I
guess it is probably the oil pressure adjuster.

What should I do to fix a meak mixture? I will get the make and model
of the boiler also when I get home and post it later on to-night, I
think it is a Riello but I will check to make sure.


Riello make a couple of basic models of burner. The old faithful which has a
grey plastic control box sitting on top of the motor and is available in a
range of outputs with slight detail changes for the various ranges, or the
recently introduced RDB range with a black plastic control unit mounted to
the left as you look at the burner from outside the boiler.
Assuming your unit is the earlier of the two since it has needed a motor
bearing then you can adopt the following procedure bearing in mind that this
will need test gear to do it right.

1. Isolate the electrical supply and close off the oil supply valve Check
the oil filter and renew paper filter elements.
2. Open up the flue access plate/doors to gain entry to the combustion
chamber and flueways.
3. With brushes and a scraper clean all surfaces, removing any baffles or
retarders to allow access to do this.
4. Vacuum out any deposits (soot and sulphur) you have dislodged.
5. Check the inside for corrosion or defects.
6. Reassemble, making sure all seals are in good condition and make a seal
but do not overtighten and distort the joints.
7. Remove the burner from the mounting flange by undoing the retaining nut
at the top of the mounting flange.
8. Withdraw from the boiler (on some boilers this may require you to
dismantle some casing)
9. Loosen the blast tube retaining screws located at either side of the
blast tube into the cast burner casing and remove the blast tube from the
burner. This will expose the nozzle and electrodes for cleaning. Note
carefully the position and clearances of the electrodes with respect to the
nozzle, compare with the settings given in your manual.
10.With a nylon pan scourer clean up then electrodes and nozzle mount. etc.
Renew the nozzle with one of the same capacity and spray angle (this is
stamped on the flats of the old nozzle for typical example 0.65 US GPH 60
degree spray angle). Removal of the nozzle may require you to loosen the
electrode block so be sure you know where to put it back again.
11. Clean out the aperture in the casing which you see behind the blast tube
and note the photocell lens is clean
12. Reassemble the blast tube and secure with the two screws. (You did put
the electrodes back didn't you?)
13. Undo the three screws holding the fan volute casing in place and expose
the fan for cleaning with a stiff bristle brush. (Some models have a
hydraulic ram which operates an air shutter over the air intake and this may
need the mounting screws removing first to allow the volute casing to be
removed). Clean the volute casing and the air intake apertures also then
reassemble.
14. It is not normally necessary to remove the oil pump unless there is
obvious sign/sound of bearing or coupling wear however if it is judged to be
necessary then loosen the two (sometimes three) screws which clamp the pump
into the end of the motor, remove the solenoid from the top of the pump,
disconnect the oil pipe nuts and gently rotate the pump a little to
disengage the oil pipes and withdraw it from the end of the motor. Check the
bearings and the condition of the plastic drive dog which transmits rotation
from the motor shaft to the pump. The motor bearings are sealed but a little
light oil may be applied to inhibit corrosion.
15. Reassemble and check your oil joints.
16. At three yearly intervals renew the oil flexible pipe, sooner if it
shows damage.
17. Obtain a suitable pressure gauge reading 0 to 250/300 PSI. Remove the
hexagon plug below the pump pressure adjuster and fit the gauge to this
port.
18. Refit the burner to the boiler and open the oil supply valve. Check for
leaks and rectify if necessary.
19. restore power and set the controls to call for heat. The motor should
start up and run for a few seconds before opening the oil solenoid with an
audible click and the burner should fire. If it does not fire the controls
will register lack of flame and the unit will shut down and go to lockout,
lighting the lockout alarm lamp under the reset button.
20. Check the pressure gauge and adjust to the specified pressure given in
the boiler/burner data sheets using the adjusting screw on the pump. Once
set this screw should NOT be touched again.
21. Situated (usually on top of) the boiler shell you should find a flue gas
sampling point. When the boiler has warmed up insert a smoke tester
(Baccarach pump) and draw a smoke sample. This should be zero on the
Baccarach scale in most cases (no smudge visible on the filter paper the
sample is drawn through)
22. Insert an analyser probe into the sample point. Either an electronic
tester or a Fyrite/Briggon wet tester sample pump tube. If you haven't got
either of these you will be unable to go further and should seek
professional assistance. Draw the sample into the tester and read the CO2
content of the flue gases. Adjust the air slide/shutter to give a figure in
line with that given in the boiler specification sheet.
23. Recheck the smoke is still within tolerance
24. Insert a thermometer into the flue sample point - this may be included
in the analyser probe if you are using an electronic set. Allow the reading
to stabilise and record. By reference to tables or from your analyser set
the nominal efficiency of the boiler can be obtained.
25. If the boiler has a conventional flue insert a draught gauge and record
the flue draught for comparison with previous recordings which will indicate
any possible problems developing in the flue integrity.
26. Remove all test gear, Check for leaks, Close up and clean down

It is a useful exercise if a firestop valve with a capillary sensor is
fitted to test this by putting the sensor into a cup of hot water in excess
of 65 degrees C

Typical flue gas analyser readings
Smoke 0 to 1 Baccarach
CO2 10 to 13 percent
Flue gas temperature 190 to 230 degrees C
Flue draught 0.02 to 0.05 inches water gauge or equivalent

HTH