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Discuss Constant air in heating system. in the Central Heating Forum area at

  1. PlumbDod22

    PlumbDod22 New Member


    New to this forum and in need of some advice, hoping some of the more experienced Plumbers and Heating Engineers would possibly be able to help me out.

    Been down to look at the father in-law's heating system a couple of times this month as the plumber he usually uses has been busy. I fitted a couple of radiators for him as a favour a few months ago and whilst I was doing this he was telling me how he has to air his pump every morning in order for the heating to begin circulating. Even when he does this the circulation is sluggish and the downstairs radiators struggle to heat.

    Once I had completed installing the radiators I filled his heating system back up and stayed back bleeding as much air out as I could to see if this would sort the problem (RV35's on the flow and return in the loft next to the boiler, and air eliminator on the coil at the cylinder and through the pump screw). I also balanced the upstairs radiators hoping this would allow the water to travel to the downstairs radiators. Problem solved! For about 2 days... The system soon filled with air again and needed bled.

    This is still a constant problem and the pump needs bled every day or 2 to allow the water to circulate. Only thing is, I am at a loss as to how the air is finding its way into his system. My First thought was that it was being drawn in through the vent pipe above the feed and expansion tank, however it looks to be a combined feed and vent pipe (Never seen this before) and I see no way how air could be drawn in.

    Any help would be greatly appreciated!

  2. rpm

    rpm Trusted Plumber

    Welcome to the forum Dod. Just giving this a little bump for you as it would appear that others are preoccupied with a little game right now.
    • Like Like x 1
  3. PlumbDod22

    PlumbDod22 New Member

    Thank you
  4. Best

    Best Trusted Plumber

    First thing I think of is if there are any auto vents on the system? Especially any fitted in wrong places. They can allow air to suck into system. Turn any off manually to test if you do have them.
    Does sound like, (as it worked for couple days on fill up), that air is being drawn in somewhere when boiler working
    Last edited: Jan 9, 2017
  5. Frog67

    Frog67 GSR

    If pump is on high setting it could be cavitation due to poorly installed/designed pipe work.
    Adjust pump speed to lowest setting and see if it makes any difference
  6. Alex Knight

    Alex Knight Active Member

    Sure it's air? And not gas buildup due to corrosion in system?
  7. PlumbDod22

    PlumbDod22 New Member

    Thanks for all the replies so far!

    Alex Knight: The sheer amount that has needed to bled while I have been there led me to believe that it was air however gas build up has crossed my mind. When the heating comes on in the morning the Boiler overheats and locks out due to lack of circulation, until the pump is bled. A fair amount of air has to be bled until the pump will circulate. Would gas be present in the amounts I have described?

    Also, if it's any help, once the system is bled and circulation resumes, the heating will work without incident until it is switched off at night, and the problems will re-occur again the following morning.

    Again, thanks for the replies so far.

  8. Pipework plus

    Pipework plus New Member

    It sounds like there could be a design flaw on the F&E side, could you post a pic of the pump with the combined F&E in shot ?
  9. PlumbDod22

    PlumbDod22 New Member

    Pipework Plus: I'll take some pictures next time I'm round, however he's been quietly lately so I'm assuming his heating is working without any problems at the moment. I had started to think that maybe the water level of his header tank was lower than the top of the cold feed connection off of it,and that combined with a small leak under the floor was allowing air in along with the water when it was replenishing itself. That was what I'd planned to check next time.

    Thanks for your reply,

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