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Hot water heating - random banging

AGS Member Posts: 4
Hello all,

I just bought a house that has hot water heating. After its been going for 30min or so, I start getting random occasional 'banging' around the house. Sometimes it sounds like its coming from a rad, sometimes it sounds like its coming from a pipe.

I've bled all the rads fully so I'm pretty sure theres no air left in the system. I havent yet bled the expansion tank.

The pressure in my system right now is around 35PSI which seems too high. The water temp is around 180F when its fully going, which may be a little too high also.

Would lowering both of these solve the problem? What else could solve the problem? Loud 'wake-the-dead' banging at 4am is turning out to be no fun....


  • Uni R
    Uni R Member Posts: 663

    If your PRV isn't working, you are in a house with a ticking time bomb. You should get a pro in ASAP.
  • Weezbo
    Weezbo Member Posts: 6,232
    i agree You Need someone There \"now type\" soon.

    Even with really tall buildings and long runs there are ways to keep everything working with out banging poping crunching gurgeling hissing type noises. Trust me..that isnt even something id have you tinker with over the phone..the reality of leveled buildings etc. seems to dictate that you want someone who understands heating systems and what they cant see when looking at what they can see. the 35 pounds could be protected by 50psi relife... Call some one today ...get it to happen...bleeding the expansion tank...no uh uh leave it alone.your fuel company may have someone trust worthy on the job right now.
  • Joel M
    Joel M Member Posts: 64

    You mention 4 am as the loud banging occurring. I wonder if you have a setback thermostat set to call for heat at that time, possible the expanding pipe is too tight thru wood floor, etc causing the pipe to try to push thru the wood. Just a thought, maybe look at areas where pipe passes thru wood.
  • jim_49
    jim_49 Member Posts: 24

    sounds to me like your tridacator gauge is stuck and not giving you the correct temp. or pressure. noise could be water boiling under low press. with pockets of air in the system. replace the gauge and prv and ..... confucious says bang on the expansion tank, if it sounds hollow... or maybe it sounds full... only a real good tech. could tell for sure ... and remember the old tale ...THE SAME GUY WHO BANGS ON A SEALED VESSEL AND XCA TELL HOW MUCH LIQUID IS IN THAT OBJECT,, IS THE SAME GUY WHO WIPES HOT SOLDER WITH HIS FINGER.
  • Vinny Pisko
    Vinny Pisko Member Posts: 1
    Hot water banging

    Hi there, Forest Hills,NY,

    Your problem could be caused (among many other things)
    by poor installation (read cheap)method,that is no
    anchoring of the pipes to internal supporting wall,or
    by omitting hangers in the ceiling and lack of insulation
    As the pipes are being heated by the water,they will
    expand and rub against materials within the walls/ceiling
    My guess is that the time lapse of 30 mins.matches the
    Another nasty experience I had with banging and lack of
    heat in 2 pipe HW system required a lot of thinking.
    The aluminum finned (passive)radiators had accessible
    vents and we had to bleed the "AIR" out often.
    When I removed the sheet metal covers,I found most of
    the radiators in slanted positions towards the vents.
    As You may not know,Your HW system requires chemical
    treatment with corrosion inhibitors.This being a new
    commercial building with the general contractor on
    location,I had no choice in selection of the sub.
    responsible for monitoring the inhibitor levels or the
    frequency of the treatment.
    The sub. Gotham Chemical was adding solid Sodium Nitrite
    the system and therein lies "the buried dog".
    From my early venture into microbiology,I recalled a
    group of(oxygen hating) anaerobic bacteria which use
    nitrite as food.It gets broken down to ammonia gas which
    easily dissolves in cold water and comes out just as fast
    out of the hot water as "AIR" I bled out of the rads.
    Well the sub. was replaced by a reputable Drew Chemical
    Co.,after the initial ( more expensive but permanent)
    treatment with Molybdate Inhibitor the gurgling symptom
    disappeared overnight.
    Yep we get what we pay for!

  • AGS
    AGS Member Posts: 4

    Thanks for all the great responses.

    Yes, my thermostat is timed to go from 4am-6am to heat the house in time for mornings. 50% of the time it wakes me up though.

    I had a guy in yesterday - my PRV does need replacing, so that will happen in the next couple of days. The gauge measures 15psi when cold so I think the gauge is working okay.

    I'm going to put carpet pieces under all the rads incase they are banging on the floor. There are some
    long runs of pipe downstairs that could be better anchored but in general they look reasonably well installed (and covered with old crusty pipe insulation)

    It so hard to localize the sounds - when I go downstairs they sound like they are from upstairs (ie. the rads), when
    I'm upstairs they sound like they are coming from downstairs (ie. the pipes)...

    Thanks again!
  • Weezbo
    Weezbo Member Posts: 6,232

    the expansion tank and auto fill sound like the other neglected items. it might have been an inaccurate triindicator with a bad tank waterfilland relife valve encrustated shut....the sound you heard might have been Ketteling in a boiler that had no true temperature setting indicator, so what? well, say you managed to get just the right combination of events..the noise would have stopped and your boiler would have been shrapnel in the basement walls...Good Day.
  • Jim_32
    Jim_32 Member Posts: 1
    Hot water heating-random banging

    Check that the direction of flow indicated on the zone valves corresponds with the direction of flow in the system.

    Jim ...
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