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New boiler/ondemand domestic HW system hamming problem

spacoli Member Posts: 61
I have a new Slantfin Bobcat  and Combicat on demand hot water and have a few problems.

1. The pressure relief valves leaking a little bit, but the boiler operates at 1 bar pressure as it should.

2. I have a hammering problem (sounds like machine gun) when using the domestic water ,both hot and cold.  When I used the cold water and it hammers, it activates the flow switch in the combicat and fires up the boiler for a few seconds. There is a pre installed flow check in the  Taco 0011 circulator in the combicat, but I'm not sure what flow that is supposed to stop.

I bought this house over the summer and the pipes have always hammered a bit when using the faucet. The supply lines are mostly 1/2" soft copper poorly installed, loosely hangered from joist  teed off all different directions. I'm in the process of kitchen and bath renovations and have run all new properly sized 3/4" and teed off 1/2" pex, but  I have not complete the supply plumbing as of yet. I have installed a few anti hammer on the old copper, but that didn't do anything.

Looking for some advice or help to remedy this problem.

Pictures of the install can be found here.

<a href="http://picasaweb.google.com/jeffspacoli/NaturalGasBoilerInstall#">http://picasaweb.google.com/jeffspacoli/NaturalGasBoilerInstall#</a>


  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Flow-Check valve back of boiler is in sideways.

    A Flow-check valve like yours should be installed with the thumb-screw pointing up.

    It looks as though the pressure relief valve at the output of the Combi-Cat is isolated from the Combi-Cat by a ball valve. 1.) I believe pressure relief valves must not be isolated by any valves. 2.) I thought that for hot water heaters, you need a pressure-temperature relief valve. And a P/T valve would have to extend into the heater itself. 3.) I am not a professional, do not really know the codes; but is either of these valves required in this setup? Better find a professional to get these three questions answered. In any case, pressure relief valves should not be leaking? Are they the wrong ones, designed for steam?

    You  might want a ball valve at entrance to expansion tank to make it easier to remove if necessary.

    Why globe valves instead of ball valves to supply and return of Combi-Cat from boiler?
  • spacoli
    spacoli Member Posts: 61
    Check valve might be the problem

    The check valve might be the problem. The hammering is coming from the check valve area, but I get no noise during heating mode, only domestic use. Not sure if that matters?

    The check valve had direction arrows, but I did not know the was a specific installation orientation. Is that orientation (thumb screw up) for operation of the thumb screw in gravity situations or is it a must to install with thumb screw up at all times?  Changing it shouldn't be a problem if necessary.

    The gate valves is just what I had.

    The pressure valve that is leaking was supplied with the boiler.

    The rest of the system component layout was was installed per the boiler and combicat instructions.

    See page 27 and 4 on the combicat.



  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Check valve

    I do not know if the misoriented check valve is causing you "the problem", but it will cause it to not work. The active part of the valve is a weight, and it is now in sideways. Nothing there to make it close.

    "The pressure valve that is leaking was supplied with the boiler."

    Is the system pressure at 1 bar when the pressure relief valve is leaking?  For most residential hot water boilers, those valves seem to be in the 30 psi range for boilers that are run around 15 psi. Or do those valves leak only when the boiler is running? I suspect that either the expansion tank is too small, that its diaphragm is damaged, or that the air pressure under the diaphragm is too low.

    As far as the rest of the plumbing, remember I am not a professional. I did see the diagram of the CombiCat. My unprofessional opinion is that either you do not require a pressure relief valve in your locality, or it is not code because you could shut off the ball valve that isolates the valve from the heater. Where I live, a pressure-temperature relief valve is required and this must be installed directly at the top of the hot water heater tank. Since yours has no tank, I do not know what the code might say.
  • spacoli
    spacoli Member Posts: 61
    Pressure tank

    It's only the pressure relief valve on the boiler that's leaking. I'm not sure when it's leaking, I'm guessing when it's running. It's not leaking much, it just must be drips a little at a time because there is just signs of leaking, not a bucket full or anything like that.

    I was thinking the the expansion tank might be the problem. I never checked the pressure. It said it was pre charged to 12 lbs. As for the size, I wouldn't know, that's the size the plumbing supplier give me when I told them what it was for.

    I'm not worried about the combicat PT. I just thought since the instruction mentioned it I would add it to be safe.

    Thanks for your input.
  • spacoli
    spacoli Member Posts: 61
    Changed the check valve

    I changed the check valve to the correct orientation and the extreme hammering (machine gun) has stopped.

    I still get the minor hammering when turning on the faucet and the activation of the flow switch on the combicat and turning on the boiler for a couple seconds. I'm hoping that will go away after the new supplies are up and in use.

    I have not seen any signs of pressure relief valve dripping. Maybe the hammering was causing that also.

    My wife was just making fun of me because I misspelled "hammering" in my original thread title. I didn't even realize. 

    Thanks for you unprofessional help. (wink-wink)
This discussion has been closed.