Not turning off your boiler when you are expecting an oil delivery is a common cause of breakdown call-outs and can shorten the life of your boiler. Why...


Because the delivery can stir up sediment &/or water from the bottom of your tank which, if the boiler is running, can get sucked up into the pipe and clog your filter - or worse, cause damage to your boilers oil pump.


But don't you only get sediment in old steel tanks?  


No, sediments and water form in all tanks and starts forming as soon as you start using the tank.  Here's why...


Without even looking at faulty seals, damaged vents, poorly fitting lids or even simply leaving the lid off, which can all cause water contamination from rainwater.  All tanks (unless insulated) develop condensation by the heating and cooling effect of day/night on the oil & tank.  Over the day the tank and oil heat up and a little bit of the moisture within the kerosene evaporates into the airspace in the tank.  At night the tank cools more quickly than the oil and the gasses in the airspace, so any moisture within these gasses condensates on the inside surface of (cooler) tank wall.  The same way as the condensation used to form on your windows (for those of you who lived pre-double glazing) and made a puddle on your windowsill, droplets form and run down the inside of the tank wall, and as you know water is heavier than oil, so the water droplets accumulate over time to form a water layer beneath the oil at the bottom of the tank.  


As in all stagnated water, algae & bacteria/micro-organisms develop. These multiply as more water condenses & sinks and as the oil breaks down naturally over time.  This algae/micro-organisms are what we see as the sludge you find in all heating oil tanks.  A common misconception is that it is delivered in with the oil, it is very rarely the case.


So, if you want to keep your boiler happy...


Always turn off your oil boiler the day you are expecting a delivery - in the morning if your delivery will be when you are out, or your delivery driver is keen and cracks on with the job without knocking first.


Leave your boiler off for as long as possible after the delivery (at least a couple of hours) to let any contaminates settle back to the bottom of the tank.


Know the state of your tank contents by using an engineer who (in line with OFTEC guidelines) inspects your tank contents for water as a routine part of the annual service.