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    • BillG100
    • By BillG100 10th Dec 17, 5:32 PM
    • 15Posts
    • 4Thanks
    Vaillant Ecotec boiler losing pressure intermittently
    • #1
    • 10th Dec 17, 5:32 PM
    Vaillant Ecotec boiler losing pressure intermittently 10th Dec 17 at 5:32 PM

    My Vaillant Ecotec boiler is losing pressure intermittently but quickly and only when it is switched off! What happens is...

    1) The boiler runs fine for a period of time which could be a few days or weeks and the pressure is reasonably constant (varies about 10% to 15% with the temperature)

    2) Boiler loses pressure quickly during the overnight period when heating / water is off

    3) Boiler won't restart and an f.75 error code is displayed

    4) I add some water to re-pressurise and it starts again without a problem

    5) The cycle (steps 1 to 4) then repeat

    The expansion vessel has been re-pressurised. There's no sign of a leak and it would have to be an odd one to behave in this way. The pressure gauge reading appears to be correct.

    I'm at a loss. Any ideas?
Page 2
    • BillG100
    • By BillG100 10th Jan 18, 7:11 PM
    • 15 Posts
    • 4 Thanks
    British Gas supposedly escalated the problem to leak detection on 3rd January but they've still not contacted me to make an appointment. I've already chased twice and been told they are on the case. Not impressed at all by the level of service!
    • BillG100
    • By BillG100 17th Jan 18, 4:43 PM
    • 15 Posts
    • 4 Thanks
    Would anyone like to hazard a guess about this behaviour:

    1) Isolate one of the five underfloor heating circuits (uhc)
    2) Pressure on boiler continues to fall over a 24 hour period from about 1.4 to 0.9
    3) Switch uhc on because I assume that's not the cause of the problem
    4) Repressurise boiler BUT this time it takes a LOT more water than it usually does to get from 0.9 to 1.4. The tap needed to be switched on for about 12 secs rather than 2 or 3.

    PS: Leak detection are in on Monday.
    • Alex1983
    • By Alex1983 17th Jan 18, 5:17 PM
    • 714 Posts
    • 410 Thanks
    I’d guess it’s more volume of water.
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