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Discuss Help! Vaillant boiler not working after changing out a radiator in the Central Heating Forum area at UKPlumbersForums.co.uk.

  1. Marty1979

    Marty1979 Member

    Hello guys.

    Please can you help as at wits end. I've changed out 4 radiators over the last 12 months in my house and the last one being yesterday. I now have a F75 code and a S98 information code on my vaillaint Pro eco tec 28 combi boiler.

    I had a GSR installer friend come over and he bled the pump and auto air vent which worked for about half and hour. When the missus went to put heating on via remote control thermostat it went back to F75 mode again!

    I've bled all radiators starting bottom to top and there is an cold standing pressure of 1.1bar

    Is there anything simple that could be done to alleviate this problem as have no hot water or heating. All other rads were no problem just this one.

    Thanks all very much

  2. CBW1982

    CBW1982 Plumber GSR Top Contributor!!

    The simplest thing you can do is get a gsr engineer who works with Vaillant's.
    • Agree Agree x 1
  3. Harvest Fields

    Harvest Fields S. Mod Trusted Plumber GSR Top Contributor!!

    Normally F75 is easily fixed for an engineer that works on vailllants a lot.
    • Agree Agree x 1
  4. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    F75 very common but you need to be gas safe
    • Agree Agree x 2
  5. AMGasServices

    AMGasServices GSR

    Try putting the pressure up to 1.5 bar if it works it will get you by for a couple of days but you will need an engineer to sort the underlying issue.
    • Like Like x 2
  6. Millsy 82

    Millsy 82 Plumber GSR Top Contributor!!

    Pressurise it to about 1.5-1.8. I found vaillants dont like 1 bar and need that extra bit of pressure to work otherwise you will constantly have problems with f75 no matter how many times you replace the part that causes it.
  7. Marty1979

    Marty1979 Member

    Thanks mate, so when the heating kicks in it will raise the bar pressure higher. So do you think that'll be OK on the radiators etc? Once raised to 1.5 bar cold do I need to bleed the rads?
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