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Kingspan Thermomax DF100 - air in the system?

  • 25-02-2022 5:07pm
    Registered Users Posts: 584 ✭✭✭ Wally Runs

    Hi Everyone, hoping you can help.

    The set up

    I have 10-year-old thermal solar tube set up (Kingspan Thermomax DF100, 30 Tubes). It has a long run from the roof to the tank, I am guessing 10-13 meters. I have had issues with the system in the past, with leaking joints and these are far as I can tell have been resolved. The results of these leaks has been air in the system, interrupting the coolant flow.  I have had the system purged a number of time over the years to remove the air the system and it has run fine for a time.

    The issue

    That during sudden sunny spells the systems seems to act as if there is air in the system. Heat builds up on the tubes, the pump is running, and the pressure is building up in the system. The fluid does not seem to be pulling the heat from the tubes. You can see the temperature differentials are wrong, with no heated fluid returning from the tubes. Eventually it goes into error mode. If I give the Temperature Reducing Vessel (expansion tanks?) a good thump, it does seem to correct itself, as if an airlock is being dislodged. The system then draws heat from the tubes and the pressure drops, everything back to normal.

    It is taking a few more thumps each time to correct it. I assume there must be air in the system collecting in the expansion tanks and or the tanks have a fault.


    1.     Do the expansion tanks fail? I understand that they are bladders, are there any mechanical parts that might fail?

    2.     Is it more simply just air still getting to the system?

    3.     Is it an affect of having such a long run from the tubes to the tank?  I recall 15m was the max recommended for this system?

    I know I can have the system serviced and purged, but it would be good to get the bottom of the issue.



  • Registered Users Posts: 3,135 ✭✭✭ John.G

    What is the system pressure when cold?

  • Registered Users Posts: 287 ✭✭ spose

    Yes expansion tanks fail. The pressure changing is a sign of that. The air is another sign. If you push in the valve on the back of the expansion tank for a second you’ll see if that has pressure in it or if water comes out you know it’s gone

  • Registered Users Posts: 3,135 ✭✭✭ John.G

    IF the system pressure is < 0.5bar, then easy to check the air end pressure, if no or low pressure, I would then pump it up to 2 bar (as measured at the air end) the water side should then read 2 bar as well, if not, either the system has lost water or the diaphragm is stuck in the expansion vessel.

  • Registered Users Posts: 584 ✭✭✭ Wally Runs

    Hi John, when cold it is just below 2 bar. It goes up to 3 when the flow is interrupted. If by the valve at the back of the vessels you mean the yellow cap. When I turn it I get fluid?



  • Registered Users Posts: 3,135 ✭✭✭ John.G

    The yellow valve is a PRV (pressure relief valve) and is set to 6bar. Your pressures are also OK at 2.0bar cold & 3.0 bar very hot.

    You should also have a flow tube showing the flowrate when the pump is running. If this is showing a reading then more than likely air in the system up high in the collector(s).

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  • Registered Users Posts: 287 ✭✭ spose

    On the bottom of the expansion tank there’s a plastic cap. Unscrew that by hand and there’s a tyre valve underneath it. Give it a small push and see if you get air or water out.

  • Registered Users Posts: 584 ✭✭✭ Wally Runs

    Many thanks, looks like I need to get the plumber out.