If you have a new account but are having problems posting or verifying your account, please email us on for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact

F&E Tank Overflow Question

  • 11-06-2024 1:08pm
    Registered Users Posts: 425 ✭✭


    Cards on the table: I don't know much about plumbing other than what I've looked up on youtube ….

    However, we have intermittent dripping outside from the F&E tank overflow pipe.

    From my research, the worst case scenario seems to be a pinhole in the coil in my cylinder, heated from my oil boiler I believe.

    My question: I have a triple coil cyclinder, and I'm fairly sure one of those coils is unused. Would it be possible for a plumber to blank off the coil with the pinhole and connect up and use the other one instead?

    Just wondering if there would be an alternative to replacing the cyclinder. It was expensive but I think the 10 year guarantee has expired.

    Thanks a million. More detail available if needed, but I'm just curious about the theory of it for now.



  • Registered Users Posts: 1,405 ✭✭✭dathi

    did you climb into the attic and check the ball cock to see if it is not shutting off properly

  • Registered Users Posts: 12,398 ✭✭✭✭Calahonda52

    an alternative possibility is that there is very little free board between the top of the water when tank is filled and cold, and the overflow pipe so when waster heats and expands it over flows.

    This would point to a leak somewhere, not necessarily in the coil

    moving the coil will work but it will reduce the volume of HW if you are moving up

    “I can’t pay my staff or mortgage with instagram likes”.

  • Registered Users Posts: 425 ✭✭Manuel

    It seems ok …. to me. No leak visible from the valve and ball cock seems ok. I haven't actually caught it in the act of overflowing in the attic (yet) …

  • Registered Users Posts: 425 ✭✭Manuel

    Thanks. The water level in the F&E tank is RIGHT up to the overflow, so it wouldn't take much to tip it over into the overflow. Should I try and get the level in the F&E tank down a bit? I've tried bending the ball cock arm down but I'm afraid of breaking it (or I'm just too weak :-) ...)

    I thought I might find/witness the expansion pipe overflowing down into the the F&E tank, but I haven't (yet).

    We recently got Solar PV installed, so that is heating the immersion all day long. That might be connected to the issue?

    Thanks again.

  • Registered Users Posts: 425 ✭✭Manuel


    Ok, I've established that this overflow happens when the central heating is on. I had put a large basin under the overflow outside last night and my daughter was woken up by the splashing at 6.30 this morning, which is shortly after the central heating timer kicks in. Then just to confirm this, I switched the central heating on manually and after about 15 mins, water started streaming out of the overflow pipe outside.

    When I went to the attic there was no water coming down from the expansion pipe above the F&E tank, but I could see under the water in the F&E tank that the were was flow coming back in from the cold water feed to the boiler.

    So, my understanding is that the heated water is getting pushed back up the cold water feed pipe. If there is a pin hole in the coil, then it's no longer a closed system and there is always extra water coming in from the cylinder and being pushed up when it is heated.

    This would explain why it also happens during the day to a lesser extent, as the solar pv is heating the immersion, which I guess is a bit slower to heat the water in the cylinder than the central heating is.

    So I guess I'll get a plumber out to see if he can blank off that coil and use the spare one instead. I might as well use it when I have it?

    Thanks. This video on youtube is what I've been basing my assumptions on:

  • Advertisement
  • Registered Users Posts: 38 declan b

    its not a pin hole in the coil in the cylinder. its a heating and F and E tank issue

  • Registered Users Posts: 3,495 ✭✭✭John.G

    Can you see where the cold feed and vent are connected into the system, if you have a heat only boiler with a external circ pump, can you see if its installed on the boiler flow or return piping, post a photo of this pump while running if it has LEDs, if not check speed setting.

    Gas or oil fired boiler??

  • Registered Users Posts: 425 ✭✭Manuel


    Oil-fired boiler. Not sure I'll be able to answer the rest but I'll have a crack at it tomorrow Thursday.