Bleeding a Firebird Popular 90 oil boiler

By The Helpful Engineer / On / In Technical & Discussion

I received a query from a reader today asking how to bleed air from a Firebird popular oil boiler. This stems from a previous article on servicing oil boilers, see here. I thought I might as well share the answer with you as it quite difficult to locate the correct nut to loosen if you are unfamiliar with the boiler.  It certainly took me a while to find the right location when I accidently ran out of oil a few years ago. See photograph below for a guide.

The photograph shows a side view of the boiler burner and pump unit. The bleed nut is shown clearly and, using an allen key, it is easy to loosen it to allow the trapped air to escape. When all the air has escaped some fuel will start to leak out, once this happens, re-tighten the nut. Press the red restart button and the boiler should restart, you might have to press it a few times.

Please note however it is easy to loosen one the wrong nut by accident, these are shown in the picture also. These nuts will bleed the system but will also cause problems with the flue/air mixture  settings (upper nut) or allow too much flue to escape (lower pressure gauge nut).

Bleeding air from a firebird popular 90 oil boiler

93 thoughts on “Bleeding a Firebird Popular 90 oil boiler

  1. thanks so much for this article
    Normally myself and the husband kill eachother when doing something like this.
    So we emptied the shed and i left him to it
    After many hours and bad language we google-whacked it
    and your article was top of the pops
    The heating is blasting , the child is warm
    Johns bleeding but happy

    thank you so much

  2. Thanks very much for posting this thread, I wasted a lot of time looking for the bleed nut and tried every nut other than the right one, which leads me on to a question. I have a new (1 year old) Firebird c26 Boilerhouse, slightly different to the pictured boiler, and I loosened the lower nut (pictured above) on my boiler while I was trying to release the trapped air. The boiler is now firing as it should be, but will I have done damage, or, will it now be damaging the boiler because I loosened the nut for attaching a pressure gauge? Thanks again for the post.

    1. Hi Miles,

      I’d say you didn’t do too much damage, but you have probably affected the air mixture settings and upset the burning efficiency of the boiler. I would recommend you get it serviced to check this and any other issues.

  3. I have a firebird popular 90. The rads are only heating upstairs since we turned the heating back on this week. I believe it may be a pump issue but I have mo idea where the pump is. Can you help please? Thanks Amanda

    1. Hi Amanda,

      The pump is usually located adjacent to the boiler, but it would really depend on your specific installation. You should involve a qualified plumber to sort this issue out for you.

    1. Hi Liam,

      The oil tank should be higher than the boiler to avoid pumping the oil to the boiler. I suppose you could raise the tank but its a big enough job if the tank is full. So maybe you could install a fuel pump, but really you would need to get a boiler technician involved to inspect the existing set-up fully and recommend a solution.

  4. Thanks v much friend for the help. Just showed off my awesome man skills to my girlfriend and shes dead impressed.

  5. Thank you so much for this! Without the picture I would have been lost and in the dog house with the girlfriend. You have helped me earn much needed brownie points! Regards, Lorne

  6. Hi I have undone the bleed nut and nothing comes out….. it has in the past….any ideas as to what should i do

    1. Hi Vicky, did you find a solution to this problem? I try to loosen my bolt too but no air/oil coming out 🙁 Thanks, Denise

          1. Yes!! Used a vacuum hoover to draw out the air and fuel like it suggested in another post somewhere worked!!!

  7. Hi there. I have a firebird boiler. It ran out of fuel. \tried pressing reset a few times before realising it was out of fuel. I have filled up and bled it as described. It is a newer version with the bleed screw on a long hex nut. I have oil coming through but when you press reset it won’t go. When the pump kicks in it sounds as if it is still getting air through but there is none when I bleed it. Any other suggestions?


  8. Having cleaned the photocell it now doesn’t lock out at all and keeps on purging and cycling. The pump is hot after a while of this. I assume this is something more sinister?

  9. Sorry for the trickle of info, but hopefully it will lead to a quicker solution. The pump seems to be working as the bleed runs very fast when it kicks in.

    1. Hi Will,

      Not sure what exactly is wrong, but I’ll try to help if you haven’t got the burner running already at this stage. When you listen at startup or after pressing the button, the fan and oil pump start first, after a few seconds the high tension electrodes produce a spark, shortly afterwards there is a click, which is the solenoid valve opening to allow the oil through the nozzle. When the photocell is defective, there are usually no sparks and no click, it locks out before that.
      After that it could be dirty electrodes, and a replacement Nozzle is no harm either. Of course, the control box itself or the oil pump could be defective, but they are more expensive to replace and usually don’t give a lot of trouble.

      Hope this helps,


  10. Hi Will,
    I have a firebird 50-82 boiler,it is 6 years old and i dont know what is wrong, i put 300 litres of oil in the tank on the 21st of november i have the boiler on for about 6 hours a day,and i have just run out of oil,this seems very bad to me,any ideas why i am using so much oil.

  11. I have a firebird 82 boiler and have the same problem as John. Got 500 litres of oil a month and a half ago and it has now ran out. Got an emergency fill of 200 litres there, tried to bleed it but there is nothing coming through at all. Anyone any hints?

    1. Hi Neil,

      I am not sure as there are a huge amount of variables. It could be as simple as an oil leak (although I hope not for environmental reasons) to something more complex. The first step would be for you to get a fully qualified oil boiler technician to investigate the problem.

      1. Hi guys you could have a faulty frost stat causing your boiler to tun constant therefore burning 24hours a day instead of 6

  12. hi, i loosened the nut with an allen key as described but no air/oil comes out. i waited a minute or so but nothing. how long should i wait? thanks in advance.

    1. Hi Ian, just wondering if you found a solution I am having the same problem 🙂 Loosening the nut but no air/oil coming out. Thanks, Denise

  13. Hi Will,
    I have a Firebird Popular 90 Boiler. I ran out of oil a few weeks ago but managed to get the boiler started after a few attempts with restart button. Last night I came home and the radiators were stone cold although the heating was set to come on on timer.
    I went to boiler and there is not even the normal red light showing on the restart button. When I press it nothing happens although there is plenty of oil in the tank which I checked. The are very snowy conditions at the moment in my area and I am worried that the pipes have frozen or will freeze.
    Does this seem like a simple bleeding of boiler situation? I have never done so before but intend to follow your instructions above when it gets light.
    Failing this, is my only option to call someone who services boilers?
    Any advice welcome-great to have something like this to refer to by the way.
    Many thanks,

    1. Louise,

      There could be many problems Air in the flue line (see here), no electric power to boiler etc. Its worth getting someone in to have a look, fix it and service it at the same time.


  14. I loosened the wrong nut by mistake, while trying to figure out how to bleed it. I loosened the top air/fuel mixture and now it won’t ignite.
    Is there any way to correct this or do I need a service?

  15. hi only got boiler to work when I loosened the nut you have marked for “attaching a pressure gauge” this bleed the system.

  16. Hi! Thanks for the article. I hope you still monitor this query! I have an airlock in my boiler. Thanks to your picture I was able to locate the correct value to open. However, even though I was successful fuel came out. Could you please advise me?

    1. Hi Patricia.

      Presuming there is oil in the tank it sounds like the fuel line might be blocked. Also check the fuel filter on the line.

      Best of luck.


      1. Hi! Thanks for that. Yes, there’s oil in the tank now. But it did run out. The last time it ran out and the boiler locked out, I was able to restart without having to bleed the line. The motor just seemed to pull the oil along. Not this time though.

        I don’t know where the filter is. Is this something I could do? I don’t mind getting stuck in…..or is it time to call for a service?


        1. Hi Patricia
          Just had the same problem the line wouldn’t bleed when I loosened the bleed nut with an Allen key
          So I used a vacuum cleaner to suck the fuel through the line and hey presto the fuel came out retightened the nut and up she fired hope this helps.

          1. Eamon you are a genius I was pressing that red button for the best part of a half an hour and no oil or air came out so i decided to give your mad idea ago and you know what as you put it “hey pretos” and the oil came out I’m now nice and warm thanks to your help cheers bud 🙂

          2. Eamon, Thank you very much 🙂 I was reading my way down having sat here for ages waiting for the fuel to come through when I got to your comment. I happened to have an old vac right next to me, so cupped my hand around the end of the vac and the hole shown in the pic above, and voila within 15 seconds I had oil through! I’ve got a little tap on the oil line so I was able to shut it off and put everything back together. Opened the line and gave it a final bleed with the cap half a turn open, pressed the red button and heating was restored once more. Fantastic, I love solutions like this 😀

          3. omg the hoover trick has just saved me from a huge engineers bill and an awkward situation as we’re mid pandemic. Thank you to the genius who came up with the hoover idea. I am clean, warm & forever in your debt!

  17. What a Great Web site…..I have been using the bottom NUT for years……Total amount of times used apx8. Now it has shred the thread on the receiver [where it goes in].

    What can be done about this?

    Thank you.

    1. Hi Mick,

      One solution would be to use a tapping tool to re-bore new threads in the original bolt hole and then seal this with a slightly larger bolt/ nut (to match the newly enlarged hole). It would be easy enough to do once you had the right tools. Maybe the first thing is to check with a boiler service technician and see what they say.

      Best of luck,


  18. Hi Will
    great site thank you. I moved into a house and the top gauge bolt is missing. A self tapping screw is in there. I wonder if it’s possible to replace the whole unit- the entire block with red arrows in your picture. This would be the silver circular part and the brown slightly rusty square part, if you follow me! If so what’s it called.

  19. Hi i have a firebird popular 90 boiler,i unscrewed the mixture screw by mistake.can you give me a rough setting or how many turns if screw roughly to set it as getting red light sinve i moved it by mistake. Thank you very much

    1. This retired engineer fella says as a rough guide screw in the top oil pressure screw all the way in and 15 to 17 half turns out .. should give a rough setting – but of course it should be checked properly with a oil pressure gauge. I have a grant euroflame 70/90 boiler fitted with a Danfoss 80EH oil Nozzle and that should be around 8.5 bar of pressure, but if you have a different nozzle it could be a completely different bar of pressure required.

  20. I have the same boiler as pictured popular 90, I recently got it serviced and it was in a worse state than yours, the baffles were very corroded, since the service the boiler is humming loudly, the eng said this is because of the worn baffles, causing air to flow too fast through flue, can these baffles be replaced or do you have any suggestions,
    Kind regards muchael

  21. Hello, We ran out of oil and got airlocked. We opened up the housing and took off the pump cover, but the nut you point to is not on ours. That side plate is smooth with only the 4 screws holding it in place. What now?!?! Everything else looks identical, except for that and there is a small metal tube at the bottom of that part which comes out of it and just ends.

    Any suggestions please?

      1. …and the only other markings I can find on the pump are:

        RBL 530SE *23

        RBL 517 SE

        Does any of this help?

  22. Hi,
    I have followed your instructions above in order to fix what I thought was a airlock in my firebird popular 90 boiler. I found that no oil was seeping through and i am still left with no heat as the burner cuts out after a few minutes when I hit the red button.
    I really don’t want to have to call someone because i only had it serviced recently.
    My oil had ran out and I didn’t realise, so I refilled it just above the tap outlet therefore I am having this problem.
    please help me.

  23. Hi
    I just got my firebird superq 90 serviced and a new stat… boiler is still burning constantly unless stat moved to off position. rads are red hot when burning. stat on min??? Any ideas why she isnt cutting out at temp?

  24. I recently bled my boiler however it is a different model to the one pictured above. I got it working with no difficulties however from reading the above I am concerned that I have adjusted the flue/air mixture by mistake….

    The nut I loosed did leak a small bit of oil after which the boiler fired up correctly? Would the flue/air adjustment screw leak oil or can it only be the screw to bleed air?

    Secondly is there a correct setting for that the nut used to bleed the boiler should be set?

    Thanks in advance

  25. Hi I have got a firebird combination boiler fitted with factory pumps (wilo) c/ h pump not running when there’s a call for heat from the wireless stat but will run with a direct electric feed from a socket any ideas regards Justin

  26. Hi,I loosened the top nut(the wrong 1 I may add!) and I made a mistake by taking it off,so the whole assembly came out and now no oil will come out now!have I ruined the whole thing?

  27. Hello Ive the newer version Fire Bird and I can hear the pump but no oil is getting to the rads.The tank was filled today. After bleeding it I saw a spark…the red light came on when I pressed the reset button but now there’s no red light and no spark.I really need some help . I’m happy to fix it if I’m told what to do.

  28. Hi I ram out of oil and now that I have the tank filled it seems to be trying to come on but won’t just stay fired up. What should I do?

  29. I have a 90 popular but there is no bleed valve like this one. There is an allen key nut to the side of the two nuts that are not supposed to be loosened. Is that it. Nothing is happening when I loosen it.

  30. Hi my family member! I want to say that this post is amazing, great written and include almost all vital infos.
    I would like to look extra posts like this .

  31. I have a firebird Q oil boiler, it is working ok but keeps cutting in and out, is there something that needs to be replaced?

  32. hi i have pouplar 90 firebird keeps clogging up black smoke comes out im after cleaning it out every two weeks but still the same any help pls

  33. Hi,
    Re: Riello Burner R40 Series

    Please could you tell me the correct “working pressure” of the fuel pump,
    mines producing around 2 bar +- if the gauge is accurate but nothing appears
    to be coming out from the pump so nothing at the jet to ignite?

    Please can you help?

    Thank you, Steve.

  34. Thanks a million to whoever posted the suggestion on using a hoover to suck the oil up. I’ve had this problem lots and this time tried duct taping the hoover head over the bleed valve and it worked a treat. Apart from a bit of oil in the hoover bag no bother.

  35. i loosened this nut as described, used a hoover to get it going. It did work , but now i have a leak out of this allen key bolt. Can anyone help with a reason why as i have made sure it is tight? Thank you

  36. Hi T.H.E
    Sorry for pointing this out to you publicly, but on the Oil Pump diagram above, the ” Flue/air ” mix slotted nut is in fact for adjusting the Oil Pressure delivered to the nozzle in the combustion chamber. This you would have to do if the oil used were changed from Kerosene to Gas Oil (Diesel) or the nozzle size used were changed. As the viscosity of Gas Oil (Redwood 35 sec.) is higher than that of Kerosene (Redwood 28 se.) the oil pressure delivered to the nozzle must be adjusted upward to accommodate full and efficient combustion. From memory the oil pressure needed for Gas Oil is in the region of 130psi (9-9.5 Bar). In Winter particularly when the oil temperature is cold you would need the higher pressure to get proper atomisation of the fuel. If one doesn’t have a pressure gauge to hand and the Air mix has been adjusted ( right hand side of fan chamber) to show the flame with a bluish colour on the tips of the flame, then good efficient atomisation has been achieved.
    Kevin : An old engineer

  37. Hi I have a Firebird 50/90. I did let it run out of Kerosene and was successful in bleeding the system but I could not get it to fire.
    It has a new pump and nozzle.
    I did call a plumber who arrived and within one minute had the boiler going and a hefty fee that would work out a 2400 euro per hour.
    Once again I was away and again I have been able to bleed the system so that oil reaches the pump but I cannot get the boiler to fire again. Its as if the fuel cannot get into the chamber but is stuck in the pipe and will not go any further.
    Have you any ideas on how to resolve the issue.

  38. Hi. I have a boiler like the one on the picture.
    I tried to bleed it but I used the presdure gauge nut instead. I can’t screw it back.
    Should I get a new nut?

  39. Hi I loose the flute nuts both of them in picture 2, i have tried to bleed the boiler in picture 1, but all that comes out is like a faom looking kerosene, i am starting ti thik its dirty kerosence, can ou help, please and thank you. My boiler is a Gerkros

  40. Just my 2 cents.

    When you bleed the boiler remove or loosen the bleed bold, place a jar underneath and hit the reset button, the boiler will run for about 10seconds which will include the oil pump attempting to push oil past the bleed valve (or bolt) you have loosened. The boiler will attempt to ignite, fail and cutout.
    Now, attempt that a few times until you see less bubbles or non. Refit or tighten the bleed bold. Hit the reset button and you should find adequate fuel pressure and the boiler should ignite.
    Best of luck.
    Now in my instance lots of bubbles then a small flow of oil very small I thought it wasn’t working.

  41. Hello!
    I have a Firebird 90 as pictured and I followed the image and loosened the correct but after letting my oil run out! Oil came out straight away so I sealed up again and tried resetting. It seems to fire up and then makes two loud engine type noises and cuts out again! (Sorry for the poor description!) This happens repeatedly. At a loss 🙁

  42. The picture of the bleed nut was exactly the same as the one we have on our firebird boiler so it was an easy job but then getting the oil through was quite difficult. After an hour of pressing reset button with no oil coming through I was beginning to think there was a bigger problem and after reading some more threads tried the vacuum cleaner to suck the oil through. It worked in about 10 seconds _ incredible!
    Just put the nut back pressed reset and we were away. Thanks all

  43. You’re a Star, thank you, I can now impress my fella with my (not so manly)engineering skills!
    Incidentally I didn’t get any oil flowing when I opened the indicated valve but it seems to have done the trick; after a couple of restarts the boilers going goodoh 🙂

  44. Further information if bleeding via the allen key bolt hole doesn’t work. This applies especially if you do not have sufficient oil pressure from your oil tank to your boiler. That will be the case if your tank is not sufficiently higher than your boiler and/or the length of the pipe run connecting the tank to the boiler is in any way long. Close off the allen key bolt, and instead open the lower of the front bolts for oil pressure gauge connection. This hole will suck a lot more air and oil through than the allen key hole, and at a much faster rate. My boiler absolutely refuses to be bled by the allen key method. I can only get oil to move if I open the pressure gauge bolt in the front bottom position. Make sure you have an inch deep tray below the hole, as the oil can spurt out quite fast. I remove the bolt completely and then put bolt back in and tighten a couple of turns so that it is still semi-open but will prevent the oil from spurting all over the place when I press the red reset button. If you have the bolt completely removed you make have oil spurt out past the edge of the tray. Once a strong flow of oil starts to come out around the bolt head you can tighten it up another turn or two. If you get a strong continuous flow of oil, then hand tighten all the way in. If your boiler has not already fired, then it should fire on the next reset.

  45. I have firebird popular 90 oil burner. One of the plugs beside the oil burner causes the fuse in the electrical circuit inside the house to trip. When we start it up and turn on the first switch, the unit makes a roaring sound and the oil pipes become hot so I’m guessing the heat is being generated and the oil is burning fine. But when we switch on the second plug it trips the fuse in the house. I know this means that there is an issue with the wire itself as we changed the fuse to a good working fuse in the plug but it still causes electrical trip. Also we tried using a double socket in the socket with the plug that works but that didn’t work either. Is there anything I can do myself? I’m not sure what this wire is is for but it seems to lead around the side of the unit and the one that works goes into the top of the unit into a small white box. Hope that makes sense?

  46. Hi
    I have a Firebird Enviromax C35 and recently it started cutting in/out when on. It continues to do this and the rads get hot so it is igniting. I removed the front panel and it seemed to run longer, although did cut out again after about 30 mins and then start the on/off cycle again. Any ideas?


  47. Years and years and years loosening tbe second nut and often up to an hour hunched over counting to 20 before pressing thenrestart button in hope.

    Eventually realised that this boiker is flawed if thats the design (had this thought many tines before) I did so ething about it today – I googled it and 3 minutes later left the 4mm alan key by the boiler and am a very happy man.



  48. Hi.
    My Firebird Pop 90 has started to cut out. I managed to do a reset the first time with a simple press of the red button. But I noticed a slight rattling noise coming from it. Then it cut out again last night – I tried to reset it to no avail. I dipped the tank for oil & there’s about 4-5inches of oil in it. I bled it but there’s oil flowing with no airlock. Still hearing the rattling noise and now I can’t get it to start at all. Any ideas what’s causing the rattle? And how to fix? Please & thanks in advance. Derek.

  49. Hi,

    Thanks for this article it helped me out the past few times I had to bleed the boiler.

    This time however I have an issue where the air flap no longer opens (the little piston/pneumatic thing doesn’t trigger).

    Any ideas?

  50. Hi guys I have a firebird boiler like the one in the picture. I’ve loosened the exact bit and tried to bleed the air or fuel out. Not fuel cane out and the boiler still won’t fire. Can anyone help??

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