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Discuss New Boiler & Expansion vessel - red needle very high in the Central Heating Forum area at

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  1. Xad

    Xad Guest

    I'll post the cliffnotes before as it turned into a somewhat long post:
    * boiler died end of last year
    * housing had everything replaced (regular boiler) this time last month (January). Baxi Solo 15HE installed.
    * red expansion vessle/tank fitted (attic expansion tank shut off i think??)
    * advised to check needle stays at between 1 and 2
    * red needle was around 1.5 when on all this time, now it's at 3.5
    * don't know where the black needle is supposed to be
    * red needle was going down progressively when system turned off, from around 1 to 0.6 bit by bit
    * photo below (i'll take another one what is happening during, missed that shot)

    This is on behalf of my parents who live in a housing association home, and i don't know much when it comes to anything boiler related (although i'm pretty good with other tech stuff). Boiler died end of last year so this time last month everything was upgraded by housing: boiler, TRVs, valves, pumps, timer, thermostat.

    I believe it's a conventional/regular system and before the red tank wasn't there so i'm guessing there was a secondary tank in the attic? Only ever saw the large water tank in the attic i'm guessing there was a smaller one behind for the heating.

    Anyway, the red expansion tank was fitted with the new boiler, a Baxi Solo 15HE condensing boiler. Not many instructions were given after fitting however, the installer said that the pressure gauge should read somewhere between 1 and 2 when it's on. I'm not sure whether he meant the black arrow or the red one, and i only noticed the black one today, the red one however was around 1.5 when on, however, when it was off, it was steadily climbing down bit by bit.

    I did bleed one radiator that keeps getting filled with air (in a house with 10 radiators which all work fine), so not sure if this is related to the red arrow going down. I did mention to the engineer that one radiator kept getting air in it, but he said it shouldn't be an issue any more as it was a sealed system, but it was still getting air in it.

    Anyway, today i checked the gauge when it was off, and the red arrow is all the way across to 3 1/2 and the black one at i think 0.5? This is way higher than the 1.5 or so he advised. Is this dangerous? Could something explode? What caused the sudden jump? Is this an emergency situation that needs to be looked at immediately or not a big issue that could be ignored, or something that needs to be looked at but not dangerous? It wasn't like this yesterday and everything is brand new (apart from radiators themselves and cold water tank and hot water cylinder). Also, another thing to note, sometimes the radiators make a bang/crack noise when it starts up, maybe after 15/20 minutes. I read that the noise can sometimes be caused by "steam hammer" caused by air buildup in the radiators. Not sure if this could have caused this and whether its dangerous or not.

    I left the heating and water on for an hour and everything works fine, below is a before and after photo (i'll get another one of during), and water/heating got hot, but the needles are still all over the place.

    Attached Files:

  2. Blake

    Blake Plumber GSR

    Ignore the red arrow, its the black one you need to look at
  3. Blake

    Blake Plumber GSR

    The pressure should be at 1 bar using the black arrow, this will then rise with temperature but should never go above 3 bar. The red arrow does nothing, it is just an indication marker.
  4. ne1ls0n

    ne1ls0n Plumber GSR

    the black needle is the actual pressure in system, red is a marker of where needle has been, the red needle is turnable by hand, turn it back to 1.5, if the red needle goes any higher than 3 again then there is a problem. this may not habe been set in correct place or mabye somone has moved it.
  5. pobsdad

    pobsdad New Member

    Don't worry about the red needle,it's just a marker to show where to fill to.You can move it with a screwdriver or thumbnail to 1.5.It must have got moved by accident.The black needle is ok as well.
  6. SilentMike

    SilentMike Plumber GSR

    the black needle wants to between 1 and 1.5 when the system is cold.
    If you have bled the radiator this will of been the cause for it to drop to 0.5 you need to check and top the system back up after bleeding
  7. Blake

    Blake Plumber GSR

    Shall we just keep repeating the same thing over and over again :)
  8. Xad

    Xad Guest

    Thanks for all the advice. Can the red needle only be moved if touched directly? If so, then no one will have moved it by accident (or touched it) as it's quite high up - just above head height.

    Do you just place the screwdriver directly above the centre of the gauge without opening it to reset it or do you place the screwdriver elsewhere? I recall the red arrow moved both up as well as down, so confused as to why it didn't go back down again?

    And finally, to refill to 1, is it important as to which order the valve taps are opened and closed? If so, to fill it do i open or close the tap under the red tank first or second?
  9. Blake

    Blake Plumber GSR

    The red needle has probably just moved with vibration, move it with your finger or a screwdriver. It does not matter in which order you open the black levers to increase the pressure. Open one fully, then slowly open the other and watch the needle move.

    Just tell you parents to ignore the red needle, it's only the black to concentrate on.
  10. dave1

    dave1 Plumber

    It prob just med through vibration, really wouldn't worry about the red needle.

    To restore system pressure to 1-1.5bar you need to turn the two isolation valves at either end of the silver flexi pipe. It doesn't matter which one you turn first.
    Best way open one fully, then open the other slightly so you are in control and the pressure doesn't rise to quickly.
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