Fatboise wrote:
Just wondering if anybody can help me out here. I have an oil fired
boiler for the central heating and hot water.


The boiler is 120000 Btu (35Kw) with a 0.65mm
nozzle in the burner.

A few days ago I timed the cycling on the boiler when it was up to
temperature and found that the burner was coming on for 2.5 mins and
then of for approx. 2.5 mins which I thought a bit excessive.


These boilers (at least for mine & several others I know) use an
optical flame/ignition sensor. The sensor on mine lies several inches
behind the ignition electrodes.

Your short cycling is a symptom off the sensor glass being sooted up or
dirty. On mine I have to unbolt the Riello unit (amazingly only 1
nut!) from the front of the boiler and clean the glass. I use a long
child's poster paint brush. At the same time the whole of the
combustion chamber should be scraped, brushed & vacuumed clean of soot
at the same time On my boiler, access is from the top via several lift
off plates & a few more screws/bolts.

A full service would include an instrument check on combustion
efficiency and oil supply pressure. Going rate here is 50-100gbp for a
full service.

Only do 1 or 2 DIY cleans before getting a full service, because the
condition of the electrodes and jets can deteriorate significantly over
a longer time span. Replacing these is not difficult but you do need
the correct gear. Cost of the right instruments is 200gbp up plus
regular calibration fees.

HTH