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Pressure too high after bleeding rads?

northernsoulnorthernsoul Posts: 97Member
Hi
We have a hot water boiler with original metal expansion tank and cast iron rads.

The fill valve was set at 15pSI. Normally system runs at 15 cold and 20-23 hot.

I noticed that two upstairs rads were not heating all the way across so i bled them and had air come out of 2.

Started up system and running hot it is approaching 30 and the limit for the pressure valve.

What might cause that? Did bleeding the rads cause the old tank to get waterlogged and raised the pressure? If I drain the tank to repressure will that help?

Comments

  • STEVEusaPASTEVEusaPA Posts: 2,825Member
    Maybe, and yes.
    It’s possible your expansion tank was water logged the whole time and the actual 'cushion of air for expansion was the radiator. So by bleeding it you left no place for expansion.
    So yes you will have to drain and recharge the steel expansion tank.
    steve
  • northernsoulnorthernsoul Posts: 97Member
    Thanks- it’s an old system - i bled them all in the fall and repressurized the tank for the exact opposite problem - pressure too low. Finnicky old system.
  • northernsoulnorthernsoul Posts: 97Member
    > @STEVEusaPA said:


    > @STEVEusaPA said:
    > Maybe, and yes.
    > It’s possible your expansion tank was water logged the whole time and the actual 'cushion of air for expansion was the radiator. So by bleeding it you left no place for expansion.
    > So yes you will have to drain and recharge the steel expansion tank.

    Can u remind me - I just need to shutoff the valve between the boiler and tank and then drain? I don’t need to shutoff the feed valve since I wil be isolating the tank from the rest of the system by closing the valve from the boiler to the tank right ?
  • STEVEusaPASTEVEusaPA Posts: 2,825Member
    It depends on whether or not you have an Airtrol expansion tank fitting.
    But generally yes, close valve, drain tank. But on recharge you want to keep the pressure up. You don’t want the system to lose pressure otherwise you’ll end up with air back up at the top radiators again.
    Of course all of this can be avoided by changing the steel tank with a properly sized bladder type expansion tank.
    steve
  • northernsoulnorthernsoul Posts: 97Member
    > @STEVEusaPA said:
    > It depends on whether or not you have an Airtrol expansion tank fitting.
    > But generally yes, close valve, drain tank. But on recharge you want to keep the pressure up. You don’t want the system to lose pressure otherwise you’ll end up with air back up at the top radiators again.
    > Of course all of this can be avoided by changing the steel tank with a properly sized bladder type expansion tank.

    I don’t think we have that airtrol fitting. At least not what I can see.
  • STEVEusaPASTEVEusaPA Posts: 2,825Member
    Nope just a regular valve.
    If you have a valve to isolate the tank, it wouldn’t be hard at all to install one.
    steve
  • Intplm.Intplm. Posts: 689Member
    You are correct. No airtrol fitting pictured.
    If the problem persists, do what @STEVEusaPA suggests and recharge the tank.
    If the problem shows up again, replace it with a properly sized bladder type expansion tank.
  • northernsoulnorthernsoul Posts: 97Member
    > @Intplm. said:
    > You are correct. No airtrol fitting pictured.
    > If the problem persists, do what @STEVEusaPA suggests and recharge the tank.
    > If the problem shows up again, replace it with a properly sized bladder type expansion tank.

    Thanks - I think I will try and drain and recharge now. I don’t want to have the boiler go on in the night and it climbs and blows the pressure relief valve while we are
    Sleeping.
  • northernsoulnorthernsoul Posts: 97Member
    > @STEVEusaPA said:
    > Nope just a regular valve.
    > If you have a valve to isolate the tank, it wouldn’t be hard at all to install one.

    Drained the tank - it was pretty full of water and took a long time. Recharged it and it seems to be running again in normal ranges.

    Thanks for the help-
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