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Is Radiator Sludge a Real Thing??

jac34 Member Posts: 25
I have a oil fired cast iron peerless boiler installed in 1996. It feeds cast iron radiators with a supply and return on each radiator. The issue I'm having is the master bedroom is 5-6 degrees colder than other rooms adjacent to and on the same floor. These rooms are on the second floor and there is also 2 bedrooms on the 3rd floor. All other rooms on 3rd floor seem OK so water is making it all the way up. Pressure is consistent at about 19-20 psi.

I have had several people look at it with no solution. Bled radiators, changed valves, drained down boiler, balanced system all to no solution. The only thing I can think of is those radiators aren't fully heating up. Could this mean there is sludge in there blocking flow? When you google this topic, there is a ton of info on it in the UK. They literally take the rads off, take them outside and wash out with a power washer. Gunk comes flying out and it's like new. Every tech I talk to does not believe this is the problem, but offer no solution either.

Any thoughts are appreciated as I am very frustrated with this issue!!


  • Gordy
    Gordy Member Posts: 9,514
    Was the radiator in question inspected to see if orfice plates which restrict flow had been installed?

    Is the rad in question getting warm/hot at all? If so is the whole radiator getting hot?

    Is the room in question a higher load room? Meaning maybe it has two exterior walls while the other rooms making temp have one.

    Mark Eatherton
  • jac34
    jac34 Member Posts: 25
    Not sure if orifice plates were checked. Is that right inside the rad where valve connects?

    The rad is getting warm, but seems to be at top and middle bottom is less warm. Def hotter at the top than bottom and when bled water comes right out. The one tech put a temp check device on it and it was reading about 100 F where the others were around 120 F.

    The load is similar to my son's room which meets the thermostat temp. Two rads and 3 windows. Both rooms have one exterior wall with a slight bump out on each.
  • Jamie Hall
    Jamie Hall Member Posts: 16,607
    Sludge can build up in hot water radiators, just as much on this side of the pond as the other. However, before you go to the trouble of hauling the thing out, check everything else for balance. You just aren't getting the flow through that radiator.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    delta T
  • delta T
    delta T Member Posts: 860
    I would lean towards a flow problem rather than a sludge problem as Jamie said.

    Is this a new problem, or maybe a problem that has never really been a problem until the recent prolonged extreme cold?

    Is this system zoned (how many thermostats do you have)?

    How old is the system (not just the boiler but the original system)?

    The orifices (if there are some) are typically located in the supply valve union, though sometimes they are on the return side. If you have orifice plates, you probably have a converted gravity hot water system. There are special considerations that need to be taken into account for piping and installation in order to convert a gravity system (no pump) to a pumped system. If the boiler was replaced, and was not piped correctly, it will cause flow problems.

    All this said, it is possible that it is a sludge problem, but I would think it unlikely.

    Take some pictures of the boiler and the piping near it, and maybe a picture or two of the affected radiators, and we can give you better advice.

    Where are you located?

  • jac34
    jac34 Member Posts: 25
    It’s been a problem since we moved in 2 yrs ago.

    There is one thermostat serving majority of house except kitchen/breakfast room which is separate and served by boiler/air handler.

    The system was most likely installed circa 1933. This boiler was installed in 1996. I think the mains are either 2” or 2.5”.

    Located outside of philadelphia.

    See some pics.
  • Gordy
    Gordy Member Posts: 9,514
    edited January 2018
    I suspect when new it worked flawlessly. Between 1933, and the now something changed whether in piping, balancing, or envelope.

    There may have been orfice plates in other radiators that got removed, and now it has unbalance the system.

    It was once gravity, and somewhere down the line a circulator was added. It may have not been right since that point on. The owners just put up with the imbalance.