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Banging & No Heat in Rad

BACKGROUND - I have a 2 pipe steam system in a house built in the 1920's.  The original free-standing rads have a control valve on the top and a return with no apparent trap  on the opposite side bottom.The original control valve looks like a small can of tomato paste and has an arm that you can move around in either direction.  The top of the valve has 8 indentations in it.  The arm can also be pulled upward I suspect it is to possible release pressure.



I replaced a rad in my second floor master bath with a Burnham recessed unit.  It has the feed and return on the inside bottom of the unit.  The first time the boiler came on the rad heated up nicely.  Since then, I get banging and very little heat in the rad.

I disconnected the rad to see if there was any blockage.  The rad was dry.  I used my wet/dry vac on the return piping and it was dry.  However, when I used it on the feed piping I got water. 

When I did the renovation, I added some new piping to relocate and recess the rad.  A new mud floor  and tile were installed.  I suspect that when the mud floor was installed, the pitch on the new feed piping was altered thus creating a low point for water to collect. 

Before I tear up the tile and break open the mud floor ( fortunately it is a small section in the corner of the bathroom) I just wated to get someone else's opinion.  How much pitch is needed?  I also suspect that some minimal amount of condensate happens as the steam progresses up the riser but due to pitch it just returns to the boiler to get recycled. 



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Comments

  • Jamie Hall
    Jamie Hall Member Posts: 17,036
    Think like

    steam, air, and water.  Steam has to be able to get into the radiator, and air and water have to be able to get out.



    It seems quite possible that when the new radiator was installed that a water pocket was created somewhere -- from the banging, most likely in the feed riser.  Also indicated by your getting water from the feed when you used the shop vac (good idea!).  How much pitch is needed?  Depends a bit on the pipe size, but anything less than a eighth inch per foot back to the main is going to give trouble, and I'd go with more if I could get it -- particularly if the pipe size is small or was reduced.  You will get a surprising amount of condensate in the risers when the heat first comes on (not minimal at all!) and it has to go somewhere.  The radiator itself should pitch to the outlet, but that needn't be much -- just so long as it's not the wrong way.



    Can you try changing the pitch before you tear up the mud floor?  Raise the radiator slightly or something?  Because it might be something else, and I'd hate to see you do that work if this wasn't it!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Woolman
    Woolman Member Posts: 5
    Additional Info

    The rad had a slight pitch when I originally installed it.  Trying the simplest things first, I disconnected the rad and increased the pitch to 4" per 10'. This is when I vacumned the feed line and got water.  After reconnecting it, the rad heated completely when the boiler cycled on.  There was no banging.  I thought I solved the problem by increasing the pitch to the return.  Unfortunately, the next time the boiler came on, there was banging and the rad was cold.
  • Jamie Hall
    Jamie Hall Member Posts: 17,036
    Sorry I didn't get back sooner

    but it is clear that if you vacuum the pipe out, and if on the next cycle it heats, then on the following cycle it bans and doesn't heat, then water is getting trapped somewhere in the riser.  Going to be necessary to figure out where, and then why, and then fix it...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Woolman
    Woolman Member Posts: 5
    Some Improvement

    No Problem.  Thanks for replying.  I haven't broken out the floor yet.  The banging has decreased since I increased the pitch to the return and more of the rad is getting hot.  Obviously with the increased pitch, less condensate is going down the feed.  I think I will wait to see what develops over the next week or so.

    I used the same diameter copper pipe when I extended the feed and retur lines about 2 feet to the new rad.  I suspect that the feed has a low point in that 2 feet I added when the mud floor was poured. 

    Thanks for your help.
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