Oil pipe leak

I suspect this may be a stupid question, so apologies in advance.

If there was a leak in the oil pipe (between tank and boiler), would it leak all the time?

Or would it only leak when the boiler is in use?

when the boiler is firing there may be negative pressure in the oil line, but I suspect that would cause air to be drawn in and the boiler to lock out, but I suppose it depends on the size of the leak.

Thanks for your reply.

I have arranged for an OFTEC engineer to pressure test it, but they can't do it immediately.

I had reassured myself that if the level in the tank wasn't decreasing when the boiler was off then hopefully it was fine.

But that isn't necessarily the case, then?

If the oil level is above the burner and pipe it will leak all the time.
Why do you ask?

Can you smell anything? Why do you think you have a leak? What period are you comparing?

I've been monitoring my oil usage after some work was done, by using a tape measure on my tank's site gauge.

According to my EPC, my house's heat demand for space heating is around 30,000 kWh per year. Typically, I have the hot water on for 2 hours a day and the heating on for 6 hours a day. I believe my boiler is around 20 years old. My measurements were working this out at around 10 litres per day, which didn't seem unreasonable.

Yesterday, though, I just had the heating on for 1.25 hours and the hot water on for about 2, and I measured this as 5 litres!

Tonight I sat with a book in front of my boiler. Initially it fired up continuously for 45 minutes. After that, though, it seemed to fire up for roughly 2 minutes 20 second, then shut down for 1 minute 10 seconds and kept repeating this (originally I was writing down start and end times, then I used a stopwatch). Can that ever be normal behaviour for a boiler?

Edit: sorry, no, I can't smell anything at all, although the oil pipe is underneath concrete so I'm not sure I would?

We don't know what output your boiler has, but on a reasonable size house the oil burner will consume maybe .8 US gallon per hour.....could be more, could be a little less.
For the boiler to come on, then shut off and repeat is typical when the central heating is on.....for hot water only, the cycling period will be less.
Underground leaks tend to show up eventually.....even as a rainbow pattern after rain on the surface- and kerosene sure does pong!
John

If you have a sight gauge that is connected to the oil pipe after the tank valve, you can do a test.

Turn off the boiler.
Turn off the tank valve.
Fill the sight gauge tube.
Open the sight gauge valve and note if the level falls continuously.

Of course if you have any other indicator that will not be possible.
Which part of the country are you in?