Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

viessman boiler

First winter with newly installed Viessman boiler and the overflow valve is leaking water whenever the boiler operates. Plumber has been out twice to purge lines with air. Found solder in one of the pumps also, but was removed and have not had that problem since. Just air in system constantly having to purge, otherwise loud noises in water coming through pipes. Are the two problems related?


  • unclejohn
    unclejohn Member Posts: 1,749
    Can you back up and show a picture of the extrol tank. And system piping
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 2,966
    edited November 2020
    Isolation valves on the boiler piping as they leave the boiler are essential for purging air. Omission of these valves will make an easy job very difficult.

    Often wrong, never in doubt.
  • kherring
    kherring Member Posts: 9
    edited November 2020
    Extrol tank view

  • joeba
    joeba Member Posts: 4
    1. Check tank
    2. That Air scoop not going to eliminate much air since you need about 18 inches of straight horizontal pipe for it work as designed.
  • kherring
    kherring Member Posts: 9
    can you point out the Air Scoop in my picture and which pipe should be 18 inches or more?
  • BDR529
    BDR529 Member Posts: 197
    Love the container of Fluff to catch the drips! How many here know what that is?
  • neilc
    neilc Member Posts: 1,460
    kherring said:

    can you point out the Air Scoop in my picture and which pipe should be 18 inches or more?

    the green fitting the tank is piped into the bottom of,
    looks like you're also pumping to the tank, not away,
    and the pump differential is getting added to the boiler loop adding pressure on the safety valve,
    consider it get repiped.
    do you see the difference in Alan's diagram ?
  • hot_rod
    hot_rod Member Posts: 15,017
    Try turning off the yellow handle valve near the Extrol tank, maybe the fill valve is causing a pressure increase.
    Did he check the expansion tank pre-charge pressure?
    There have been reports of tanks with the diaphragms stuck and not allowing fluid inside.

    Does the Viessmann low loss header have an air removal function, it would do a better job compared to that scoop.

    Pump on the bottom is not in an ideal location, it should be downstream of the expansion tank, but it should not be increasing pressure in the boiler.

    Does it heat okay, no valves inside the boiler turned off?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • RPK
    RPK Member Posts: 90
    Low loss header has a coin vent on top.  I think it’s 1/8” thread.  If so, it would be a great place for an auto vent.
  • TAG
    TAG Member Posts: 489
    Does that model have an internal circulator ?

    Mine needs a boiler pump?
  • The 100 series has an on-board primary pump.
    Often wrong, never in doubt.
  • kherring
    kherring Member Posts: 9
    Update on my Veissmann boiler. Plumber came out and attached new PRV on to the top of Veissmann, see photo. Also recharged Exptank.
    Now less amounts of water coming out of overflow but it is brown.