Oil central heating problem - radiators won't heat up and trying avoid paying for a call out
We ran out of oil in the summer, about June/July time. We did without until recently and got some oil delivered yesterday for the colder weather coming in. Now the radiators won't heat up at all.
I though it may have been air in the pipe, we've had that before when we've run out and I bleed the boiler myself without when that happens. After getting oil I bled it for a while (took a number of goes) til the boiler stayed on and kicked in.
When it did fully kick in, it smelt a bit stinky, like a bit of a burnt smell but I thought, since it hasn't been on in months, that would be expected. The steam/smokiness was coming out as normal and I went back to my day. Then 20 mins later or so I noticed there was no heat in any of the radiators at all. So I went to investigate. The boiler was on but no steam/smoke coming out.
I turned the heating off and put a pin in it til later after finishing work. I've tried bleeding the boiler again, I tried bleeding the radiators and I've checked that there's water in the tank in the roof space - both the main tank and the smaller overflow one above.
Today when trying to get it sorted, I noticed that the boiler comes on, I can hear it humming and the red light is no longer coming on to reset it. But the secondary firing that you normal expect to hear, and that I heard the other day, isn't happening. So it's just the lower humming from the boiler but not the louder noise that usually follows it.
I really don't want to pay someone to come out and would like to try fixing it myself but I'm not sure what to do now. I'm finding it hard to find advice online and I don't know really know how to describe the secondary firing or where or how that happens and what could be wrong.
If it helps at all, I also believe my system is gravity fed and doesn't have a pressure guage, I can't locate one but I don't even think that's the problem. I think it's boiler related - since it's not doing that secondary firing - but welcome any corrections to that.
Not sure if this is the best sub for this problem or if anyone can make sense of my explanation but I would appreciate any advice.
Edit: I am getting oil to the oil pump, when I losen the screw on the bleed valve, oil trickles out as normal and no air bubbles are coming out anymore.
TLDR: haven't used my heating in months, now radiators won't heat up. Boiler has been bled and tried bleeding radiators to no avail. Boiler stays on but doesn't fully fire up with second louder noise that normally kicks in and there is now no steam/smokiness I normally expect when the heating is on.