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Help finding and fixing leaks in old hot water CI rad system

Hi, this is my first post. Earlier this year I purchased an old (c. 1910) house with a hot water heating system and old cast iron radiators. When we inspected the house in Feb. the heat was on and worked great. Then the house was vandalized before we closed and a short section of copper pipe was stolen which shut down the system when it was still pretty cold and I think there was freeze damage before all the water was drained out. The only obvious sign of a leak we could see was a few icicles/water coming from the bottom of one of the radiators between two sections. We still purchased the house (with a large price reduction) and have been making repairs.

Recently, I had a pro in to take a look at our boiler and see what would be needed to get the system up and running. I told him about the leak and he started filling the system. We got to about halfway full on the first floor when a substantial leak started around an elbow of one of the pipes along the outside wall turning to go up. We stopped it right away and I spent the rest of the afternoon cleaning water up in my basement...

I'd like to get the leaks fixed and the system running again because the old radiators/hot water heat were one of the selling factors on the house for us. I want to know what the best way to find and fix these leaks is. Is there a way to pressurize with air so I could find them without causing a flood? Would you then just check for pressure drop and listen for hissing? Once I do what is the best way to repair? carefully cut out/remove the leaking sections and replace with BI pipe and unions? If I could at least identify where the leaks are so a pro could fix them without them spending all the time hunting them down that would probably save me a bunch. Any thoughts?

Thanks in advance,



  • McMaster
    McMaster Member Posts: 28
    I found and repaired a couple dozen leaks in my in-floor radiant system (PEX). I think you are on the right track. Filling the system with pressurized air and listening for the leaks I have found is the best way to go about it. What you will need to do is isolate each run as best you can. I made an adapter with a gauge on it with an air chuck on the end which I can hook my portable air tank to. The house needs to be completely quiet inside.

    If the leaks are severe you may need an assistant to release the air into the system while you listen for the leaks. Once you find them, you may need to cut a hole in the wall to repair. If it's black pipe and it isn't possible to get a re-threading tool in there, or find a threaded joint nearby to un-do, and you wanted to really get a solid joint, you could braze on a threaded nipple or another piece of pipe with an oxy-acetelyne torch and brazing rod. That's probably what I would do. It would be permenant. It is a lot like soldering. Depends on the tools you have at hand and your skills. There might be pro-press options available too. Good luck.

  • icesailor
    icesailor Member Posts: 7,265
    Your "Pro" must still be living and working in the Cro-Magnon Era. If someone tells a "Pro" that their building suffered a freeze up and might have broken pipes, why on God's green earth would you use water to look for it? Use air. You never have to clean up air that is leaking from a water pipe. You've already discovered what happens when you use water. Go to a volume store and buy a cheap (under $250.00) air compressor. I've seen "deals" on them where they throw in a pneumatic air nail gun in the mix. A 50' rubber air hose, air adapters that fit your compressor and any tools you might use, and make something out of 1/2" black pipe nipples, that have a 1/2" X 1/4" Reducing coupling on one end to put a male air hose adapter in, , a 1/2" IPS Ball Valve, a 1/2" Black IPS X1/2" IPS X 1/4" IPS tee and a 1/2" Bl. Coupling to put a 1/2" boiler drain into. Get a 0# to 100# 1/4" IPS "Bottom Gauge" and screw it in to the tee. Put the 1/2" boiler drain in the coupling. Put the fittings all together so that when done, the valve is between the air hose connection and the ball valve, with the gauge tee AFTER the ball valve. Get a 6" Double Female washing machine hose connection and connect it to the boiler drain. My favorite is a longer one with the 90 degree ell on it to keep the hose in better places, and not kink the hose if you need to stretch it another inch. The 50" rubber air hose (don't use a coiled plastic one unless you like to suffer and trip over it) with a male and female connection on the ends. Connect the male end of the hose into the compressor, the 1/4" male air fitting on the air tester, into the female end of the 50' air hose, the washing machine hose into any standard boiler drain in any part of the heating system, the other female end of the washing machine hose on the boiler drain of the tester, the regulator on the compressor to below 30# (25# is a good place to start) and open the air flow. If water starts squirting from anywhere, put a hose on the bottom of the boiler and let the air pressure you are adding, blow out the boiler and pipes and drain it out of the hose. When there is only air blowing out of the hose, the system is drained. Go around and listen for leaks.

    If the compressor cycles off and stays off, and the gauge on the tester says 25# (that you set it at), you have no more big leaks. If it holds 25# for an hour, you probably have no more leaks. Turn off the compressor and if the system holds 25# overnight, its tight. You will be able to hear any air escaping if you have adequate high pitch hearing. If not, find someone who does and show them what you are doing. Fix the leaks found.

    If the Potable water system froze and broke also, and it isn't fixed. turn the compressor regulator to 60# and do the same with the potable water. If you find a place where water is trapped around a leak, leave the compressor running and blow the water out with air by going to faucets downstream of the leaks. It works well to do the Potable Water System first, blow all the water out of water heater tanks, and use the water heater tank as a temporary air storage tank. You can then fill the boiler/heating system through the auto-fill valve on the boiler, maintain 12# or whatever the PRV is set at, and not have to listen to the air compressor come on and off.

    I showed this method to Clyde, my mechanic friend from Jamaica, and he was impressed. Although they don't get many frozen pipes in Jamaica, it works well for him when he does water piping. Clyde is one multitalented dude. He can fix more things that I can.

    "We learn from every person and thing we come in contact with. If we are willing to listen and learn".

    Someone I know.
  • RobG
    RobG Member Posts: 1,850
    Why is a post from September being rehashed?
  • McMaster
    McMaster Member Posts: 28
    IceSailor: Good info.
    One case where water DOES help detect leaks is in some very hard to detect minor in-floor leaks. Almost all leaks in my radiant floor occurred where the PEX touched the foam at the bottom of the slab (then can 'blow out' downwards where there isn't any concrete). Its often difficult to hear a small leak 5" below a concrete slab and if there is a seam in the foam board, the sound can travel and throw ya off. Therefore filling the isolated PEX line with soapy water and pumping through the line and shutting off the pump, the line will suck in air where the leak is and that air-bubble sucking sound seems to be easier for the ear to pinpoint. Afterwards one should flush the line with clear water.
  • icesailor
    icesailor Member Posts: 7,265
    Have you tried a stethoscope?

    Soap is hard on a heating system due to its corrosive nature, and really hard to get completely out of a hydronic system.

    My high pitch hearing is so sensitive that I hear and locate exactly where a cricket is on a room. I often hear sounds when no one else can or doesn't hear it until I point it out to them.