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Help replacing a pressure reducing valve

zvalvezvalve Member Posts: 33
I assume this pressure reducing valve is no good but can I replace it without draining my entire heating system (called drain down?)? The 3/4” pipe on the left is a return from the first or second floors and has no valve on it so if I remove the pressure reducing valve without draining the upper floors won’t water just gush out? The pipe to the right of it with the ball valve Is also a return from upper floors and I can isolate that with the valve

The cold water feed which I assume is the 1/2” pipe way right can be shut off. This is on a Dunkirk PvWB gas fired boiler. Any solutions besides drain down?


  • STEVEusaPASTEVEusaPA Member Posts: 4,216
    edited May 3
    Nope. Have to drain it. But do yourself a favor and put on a backflow preventer too, and ball valves on both sides, for easier maintenance and replacement. Use a threaded so you won’t have to solder anymore, or press fittings. Looks like you have other leaks too.
    Might want to do valved iso flanges on that circulator too, but at that point, you'd be better off properly re doing your near boiler piping.
  • HVACNUTHVACNUT Member Posts: 3,415
    Any valves on the supply? Odd only one return has a valve.
  • JUGHNEJUGHNE Member Posts: 6,985
    With the system drained is a good time to check your expansion tank pressure should be 12-15 PSI.
  • hot_rodhot_rod Member Posts: 13,526
    Yeah, where to start and stop on a repair like that. Any other valves up out of the pic? If not a drawdown will be needed. I'd start from the circulator up, also add a Webstone purge valve in the piping so the entire system could be purged from one point. I suspect the expansion tank is in a less then desireable location? On the boiler supply?

    This would be a nice upgrade plan.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • zvalvezvalve Member Posts: 33
    Thanks everyone for insightful responses. I guess I need to take courses in boiler plumbing but I have more questions.
    Hvacnut: 1. How hard is it to drain and refill a hydronic system? Can a total neophyte do it?
    JUGHNE: How can you test pressure of expansion tank? Can I do it while boiler is on and system is filled with water?
    STEVEusaPA: 1. What does backflow preventer do and where does it go?
    2. What are press fittings?
    3. What are valved iso flanges?
    4. How do you avoid cold soldered joints due to moisture present in freshly drained water pipes?
  • zvalvezvalve Member Posts: 33
    Hot Rod
    Expansion tank is on the out flow side.
    In between Aquastat and zone valves. Could I limp along with leaking pressure reducing valve for a couple more weeks until heating season is over here on Long Island New York?
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 7,099
    As long as the water is not gushing out you can wait until the heating season is over
  • HomerJSmithHomerJSmith Member Posts: 929
    edited May 4
    Just replace the expansion tank, they're cheap. I use Caleffi fill valves, I just like their design.

    You can try to tighten up the four bolts holding the diaphragm on the PRV. The important thing is that it is regulating the pressure in the boiler. Check the tridicator pressure reading for any increase between 20 to 30 psi.

    If you replace the tank it should be factory set at 12 psi and the PRV should be set at 12 psi so that the sys pressure as shown on the tridicator reads 12-15 psi. I usually increase the tank pressure to 15 psi before I install it. Yes, you have to have the tank empty to check and adjust the bladder pressure. The PRV pressure should be the same as the bladder tank pressure.

    Where is all that water staining and rust coming from on top of the boiler?
  • HomerJSmithHomerJSmith Member Posts: 929
    edited May 4
    1. What does backflow preventer do and where does it go?
    A backflo preventer, prevents the boiler water back feeding into the potable house water sys. There are different degrees of BFP's depending on the degree of hazard. It goes on the 1/2" boiler cold water supply line before the PRV. There should be a 1/2" ball valve before the BFP in case repairs need to be done on the BFP.

    2. What are press fittings? Press fittings are a way to connect pipe using a special crimp tool. The fittings have a EPDM oring in the fitting that makes the seal instead of solder which makes a seal in regular sweat fittings.

    3. What are valved iso flanges? ISO (International Organization for Standardization) are flanges that are secured with bolts.

    4. How do you avoid cold soldered joints due to moisture present in freshly drained water pipes? You heat the connection hot enough to dry the pipe connection and allow the solder to flow into the joint. It is important to make sure that the pipe and connection are open to the atmosphere so the water vapour has a way to escape. If the pipe and fitting are closed, pressure from the steam will blow the solder out of the joint as a means of escape and you will have a badly sealed joint which may leak later.

    Whether a novice can refill a sys depend on the piping design and connection to the boiler water supply. It's easy-peasy if you know how to do it. Sometimes you can use the boiler fill valve and sometime you need a pump to provide enough flow to drive all the air out of the sys. Having air vents on the high points certainly help a whole lot.

  • STEVEusaPASTEVEusaPA Member Posts: 4,216
    You should find someone on this site who is local and knows hydronics.
    Other issues you may wish to address with the near boiler piping:
    -You’re not pumping away from the expansion tank.
    -Air scoop isn’t installed correctly, and even if it was, is not very effective. A modern micro bubble reabsorber is the way to go
    -A Webstone Expansion Tank valve would make life easier, for future checking of the charge and replacement.
    -Any other ball valves to make isolation/component replacement and purging.
    -Boiler drained, might as well replace the relief valve, cheap insurance.
    It sounds daunting, but it’s really probably 4 hours max with someone who knows what they are doing, and you’ll be more comfortable, and easy bleeding/purging.
  • zvalvezvalve Member Posts: 33
    Thanks Homer and Steve. Rust on top of boiler are from leaking copper hot water pipe that came from water heater and had pinhole leaks. So to reinterate I have to completely drain the heating system in the house to work on the boiler or can I close the valves on some of the radiators in the upper floors so the system is not completely empty. How should the air scoop and expansion tank be plumbed?
  • HomerJSmithHomerJSmith Member Posts: 929
    The green air scoop should be on the hottest water, which is the output of the boiler. That is where it is, now, so don't change it.

    The Expansion Tank should be installed per hot_rod's diagram on the input of the pump. Also replace the pressure regulating valve because the old one is leaking.
  • EdTheHeaterManEdTheHeaterMan Member Posts: 636
    edited June 23
    I see one other potential problem. Two 3/4" returns are manifolded together with one 3/4" outlet to the circulator. As long as the home is small enough, there may not be any problem. If however, the design requires more than 40,000 BTU of radiators/baseboards/emitters/etc., there may be some cold rooms on the coldest days of the winter. So the question is... Are there any rooms that do not get enough heat on the coldest days (and nights) of the year?

    If the answer is Yes, then you should consider a redesign.

    If the answer is No, then just do the minimum repair.

    There are so many minor problems there that by themselves there don't present a problem. If however, you have a comfort issue in the cold cold winter nights, some simple redesign can make the existing boiler last for years and years.

    A question: What type of radiators are in the home?

    3/4"copper pipe indicates that you have Baseboard covers with Copper tubes and Aluminum Fins (called elements) inside the covers. If there are more than 65 to 70 feet of element throughout the home, then you need the redesign.
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