Help diagnose the hot water problem in our condo!

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by gee, Jan 28, 2008.

  1. gee

    gee New Member

    Jan 28, 2008
    This problem started recently. I am in a condo of six units. Our hot water is derived from two big hot water heaters, working in tandem. Recently the overall hot water pressure seems lower then before and now when someone else either yourself or someone else in the building also uses hot water, the flow is reduced to a near trickle. Needless to say this is a problem when taking a shower. A plumber has visited the scene. The water inlet pipe to the heaters is only 1/2" while the heater outlet pipes is 1 1/2". To evidently compensate, there is an electric pump on the inlet. The plumber thought the pump was defective and had it replaced although the new one seems smaller. However the problem still exists with no change in the symptoms at all. The plumber was called again and he says it must be for some reason the overall pressure of the water entering the building has been reduced for whatever reason as that can be the only explanation. The thing is unlike the hot I can run multiple sources of cold water without a noticeable drop in pressure although the overall cold water pressure is greater then the hot to begin with.

    My thought is perhaps it's something to do with one of the heaters but they merely just heat water as it's passed thru don't they, meaning it wouldn't factor in to any pressure problems?

    If there are any ideas, I would appreciate them. I know very little about plumbing and this is bewildering.
  2. Cass

    Cass Plumber

    Nov 12, 2005
    I think you are wrong about the exit pipe size. 1 1/2" is huge and would not normaly be on a water heater servicing a 6 unit building.

    If the tanks are old and they used galvanized dielectric couplings to connect to the tanks you may have one that rusted to a small enough ID that some debris clogged it. Other than that we would have to be there to diagnose further.

    If the plumber is competent he will find the problem eventually after eliminating all the possibilities one by one.
    Last edited: Jan 28, 2008
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  4. gee

    gee New Member

    Jan 28, 2008
    The pipe diameter information is what was given to me by the plumber. The dimensions may be incorrect the egress is clearly larger then the inlet.
  5. Cass

    Cass Plumber

    Nov 12, 2005
    He should check the water flow B 4 the heaters and directly after the heaters to determine if the problem is even the heaters.
  6. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    Pressure Gauges

    Pressure gauges!

    Two pressure gauges, one before the heater pump and one after the heaters, will go a long way toward diagnosing the problem.

    The pressures should be observed with:

    1. Pump off, no flow
    2. Pump off, low flow
    3. Pump on, low flow
    4. Pump off, high flow
    5. Pump on, high flow

    If the pressure is not at least 30 psi at the outlet of the heater plus 4 psi for every floor above the heater, for the case of the Pump on, high flow, then the system is defective due to inadequate supply, too-small pipe, inadequate pump, or plugged lines.

    It also must be established that the pump is indeed ON whenever someone is drawing water. The pressure at the outlet of the heater should NEVER fall below 30 + 4 per floor. There should be a flow switch because the pump should not be running when there is no flow.

    If the system is always putting out 30 + 4 per floor and there is still a problem, then there is a problem in the distribution lines.
  7. Master Plumber Mark

    Master Plumber Mark Master Plumber

    Feb 6, 2005
    Sensitivity trainer.. plumber of mens souls
    indianapolis indiana - land of the free, home of
    corroded dialectric union

    I did this same job on satruday

    I see it all the time .................

    if it has dialectric unions on the top of the heaters

    one of them is totally corroded shut....

    if their are only copper fittings, then one of them
    is getting scaled up inside........

    it is not a pump issue, its a restriction on the top
    of the heater.....

    probably on the hot water outlet side.....

    if you open the t+p valve and you have great pressure

    you can almost be sure its on the hot outlet side of the system

    he can either take and change out the fittings or
    he can put brass compression unions on the top
    of the heater and take a large screwdriver and
    hammer and rheem out those inlets and outlets......

    this has to be peridocally done and the brass unions
    make it easy to access in the next year or two

    if their really is only a 1/2 inlet to the heaters ,

    I would start pokeing around there
    Last edited: Jan 28, 2008
  8. gee

    gee New Member

    Jan 28, 2008
    Ok, different plumber came yesterday and discovered a valve was half open. Opened it all the way and pressure seemed to return. However this morning the water temperature was lukewarm at best. Plumber called back and as relayed to my condo trustee this is what he said the problem was.

    "The problem appears to be part of the mixing valve being built up with sediment over time. Basically, there are 2 hot water pipes coming from each water heater that mix with a cold water pipe to keep hot water from getting too hot. There is also another small pipe that usually backflows & recirculates the water. Right now, the water is flowing through the small pipe, restricting water pressure but maintaining the temperature. When the plumber opened the valve yesterday (it should be open in a properly working system), it fixed the water pressure problem but since the mixing valve is not working properly, it restricted the hot water from coming up. So, for now, the valve is off & the water should be warm again but the pressure will be low. The mixing valve parts are so old they have to order them. The plumber is going to call me back today & tell me when it should be in & then he can replace it. Unfortunately, there aren't interchangeable parts for this so he can't use another brand without replacing the entire system & pipes & everything else."

    Does this make sense. The thing is, he talks about a gradual build up and this problem or at least the symptoms of such appeared all at once. Anyhow we are back to square one, hot water but low pressure.
  9. patrick88

    patrick88 Plumber

    Sep 3, 2007
    Webster Ma.
    The mixing valve could be the cause of most of your problem. I have seen many plumber install a valve to choke the flow so the water has longer to get hot. I'm sure a plumber installed the valve or closed it a little to slow things down a bit. You should have the plumber do what master plumber mark suggested also. Cover all your basses.
  10. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    If the inlet pipe to the water heaters is really only 1/2", then you don't have to check any further. That is too small for any purpose, even a single person house, much less an apartment building.
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