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Burnham Series 2 problem -- water sounds in pipes

PingberPingber Member Posts: 9
I have a 3 year old Burnahm series 2 gas boiler, baseboard heating.  Each year, I have the same problem.  After the boiler has cooled off for a while (like after a long night of being off), when it turns on a starts circulating the water, it sounds like there is a rushing, bubbling river in the pipes.  Not a  knocking, like air, but rather like a bubbling brook.  After the water heats up, the sound disappears.  I've had the system bled each year for the past 3 years, but the problem comes back.  The HVAC installers have told me (at the end of the last heating season), to shut off the water feed, shut down the boiler, and watch the guage over the summer to see if it was losing water due to a leak.  It held at 20 all summer.  They now think that one of the copper pipes that runs through our slab (no basement) has a leak ... the only problem is that the pipes don;t run through the slab, they run over all of our doorways etc.  So the HVAC people are now pissed at us for calling them back all of the time, and the noises are driving me nuts.  ANy ideas?


  • PingberPingber Member Posts: 9
    ...just to let you know ...

    After a long phone discussion with our HVAC people ..., they sent out the "head" tech ... I had turned off the system to let it cool until he came ... of course, I heard the water right away, he did not (to be fair, he's an older guy) ... however, as the system heated up, he did hear what I heard.  He checked a few things and then said, if its air in the lines, we'd be hearing it also after the system heats up, but we're not.  He then looked at the circulator (which we had replaced two years ago after the original one failed after only one year) and asked if I set it on high speed.  I told him I hadn;t touched it since it was installed (and that IS when the problem started) ... he reset it to low and said it was circulating too fast and that is why we were having the problem ... so we'll see what happens tomorrow morning ... I don;t have high hopes, I think he just wanted to move on.
  • ProfProf Member Posts: 7
    water sounds in pipes

    The "old" guy could be right...without being able to see your system and actually analyze it, it really is hard to say, but the sound that you heard could've been "pump cavitation". Turning the speed down might solve the noise (and cavitation).

    Let us know how that turns out. There could be other factors.
  • icesailoricesailor Member Posts: 7,265

    Prof is right. Pump cavitation.

    If you could put  pressure gauges on the inlet and outlet of the pump, you would probably see a high differential pressure. Showing the restriction in the system. It may ne caused by excessive length runs in the radiant loops. They shouldn't be over 200' or 250'. More short loops are far better than fewer longer loops.

    I just installed a Wilo variable rate pump in my house to take care of excessive pressure when only one small zone is calling in my 5 zone valve house. I didn't have a problem that I was aware of but I thought it neat. Sounds perfect for you. 

    The only other time I have heard what you describe is on a system that was set to 12# and a warm start boiler. A seconf floor zone would come on and the sound at the first 90' ell sounded like water running for a moment or to until the water cooled down and the water stopped boiling from the cavitation.

    Submarine propellors cavitate under water. When they have a lot of thrust/power at shallower depths, they will cavitate and make noise. The sonarman listens for this. Go deeper for greater pressure and/or slow down the prop.
  • IronmanIronman Member Posts: 5,632

    If the pump's on the return line up stream of the expansion tank and you have zones valves, you may have been cavitating. The fact that the first pump failed so quickly also points to this.

    If the pump has been cavitating, checking the impeller would give proof because that is where cavitation occures.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • icesailoricesailor Member Posts: 7,265


    I know that it is a "rule" that pumps must be on the supply side of the system and not the return. The hotter the water, the greater the cavitation. There is a difference between the whole impellor having a giant bubble around it and just the tips having bubbles.

    I see this happening on warm start boiler/systems like my own houses. It all has to do with temperature and pressure, plus or minus.

    The house I live in now, has the circulator mounted as it comes out of the supply side of the boiler. Like W/M shows and the guys who installed it, did it. I didn't plumb the house. It cavitates like heck. I always install the pumps on the return. I never get that cavitation because of the cooler return water.
  • PingberPingber Member Posts: 9
    how can I tell?

    Guys -- I appreciate your answers.  It does sound like a cavitation problem, especially it disappears after warming up.  AND I do remember the installers saying something about moving the pump when the furnace was installed, due to clearance near a clothes dryer door.  Is there a way that I can tell for sure which side the pump is on?
  • PingberPingber Member Posts: 9
    oh and by the way ...

    Even with the pump on low, the pipes still gurgle in the morning until the system warms up.
  • PingberPingber Member Posts: 9

    I also forgot to tell you that the system is set for 20#
  • SlimpickinsSlimpickins Member Posts: 322
    the only real solution

    The only real solution is to make sure you're "pumping away"  I believe  Burnham still ships their boiler with a return mounted pump. I imagine you have an air scoop or some air elimination device on the "hot out" of the boiler and your expansion tank and perhaps make up water is tied in at that point. If so, the best solution would leave the air scoop where it is and plug the bottom, remove the expansion tank and make up water and install it at a tee on the suction side of the pump. Or you can move your pump so the air scoop/exp tank/make up water is on the suction side of the pump. Problem solved.
  • ProfProf Member Posts: 7
    pumping away

    "pumping away" is a term we use to describe the postion of the circulator (pump) in relation to the cusion tank (diaphram tank). The circulator needs to be "pumping away" from the cushion tank, otherwise there is a risk of having too low or even negative pressures on the inlet of the circulator. When that happens there is a good chance that there will be liquid converting to vapor (because of the extra low pressure) and then having those vapor bubbles imploding (water vapor shrinks approx. 1700 times by volume when it condenses) at or near the tips of the impellor (where there is higher pressure) creating a lot of noise, poor pump performance and very destructive forces on the impellor. This problem should be worse when the water is warmer, as the liquid will be closer to its vapor temperature (boiling point).

    The cushion tank needs to be on the suction side of the circulator.

    So, as "slimpickins" says: make sure that you are "pumping away". And if the noise persists, bring in a professional. Even if he is an "old" guy... 
  • icesailoricesailor Member Posts: 7,265
    Pumping Away:


    For the sake of discussion et-al, your idea of cavitation and mine are somewhat at odds. In a sense. Conventional wisdom (CW) now is to put the fill valve at the pressure (Extrol) tank tank. The old way was to put it at the bottom of the boiler so the cold fill didn't interact with the hot water. AND you could tell when purging, that you had all the air out when the water got hot. But saying you must "pump away", you have the circulator AFTER the extrol tank, pumping away. That makes the fill valve "see" lower pressure, Putting the circulator between the boiler and the tank, makes the tank "see" a higher pressure. If you feed the system at the extrol, and you set the system pressure for 12#, and you have a pumping differential of 5#, the fill (PRV) can see and add water. Overfilling. To me, it doesn't matter where it goes because if it is on the supply, and you design for a 20' drop, the return will always be 20' colder than the supply. Not a bad thing. But circulator in a closed loop heating system just pushes out one side and sucks in at the other. It isn't like the system goes negative. Wet rotor pumps suck when it comes to fine finishes on the vanes of the impellers. Nuclear submarines have the finest designed and finished props that money can buy. They cavitate at depth. That's what a sonar-man listens for. Each prop has a signature. It is identifiable. Slow down the RPM, go deeper or both. To be quiet.

    I see all these incredible heat jobs here. Miles and miles of 1/2" PEX. Pipes increase as do their squares. It takes 4 -1/2" pipes to equal a 1" pipe. We had tables that said that 15,000 BTUs were all that you could put through a 1" pipe. That 60,000 or 65,000 BTU's could go through a 1" pipe. Now I see 600' loops of 1/2" PEX on floor loops with high head circulators to push it through. We did monoflow jobs with 1" mains. The branches were 3/4" and 1/2" with the main tees rolled on a 45' and long sweep 90's to keep the restriction down and the flow rate up. What happened?

    The other day, I spoke with a friend about a boiler. He was having a problem getting air out of the one he was dealing with. To a pool heater arrangement. The gas boiler was rated at 400,000 BTU's per hour. Did you do it primary, secondary? Sort of was the answer. What size is the primary loop? 2" copper. I thought about it. Maybe 2" isn't big enough. Seems like it should have been 2 1/2" or 3". That maybe there isn't enough water flowing through that loop to absorb all the energy at full throttle, 400,000 BTU's and his air is a byproduct of steam. Have a M-80 Munchkin with the primary pump stopping and the secondary pumps working and see how fast it steams.

    Steamhead has a nice picture of a boiler he replaced here, But upped the outlet size to 2 1/2' from 2" I know why. Less restriction. But all that 1/2" PEX?

    I'll keep my runs short, with more. My holes large with sleeves to stop rubbing noises and I'll be able to purge through the boiler while it is running, with a ball valve on the return and a drain above. When the water gets hot after the bubbles leave. I'm done. And I won't hear any creaking and banging.

    And no cavitation

    There's a lot to be said about those old dead guys that Dan speaks of and what they did. I'm not dead quite yet.    
  • PingberPingber Member Posts: 9
    ok, so now what?

    The major problem is that I can;t get the HVAC guys to do anything except kind of walk around the unit and tell me that there's nothing wrong with it.  This has been going on for two years now.  They think I'm crazy and I know that there is something wrong .... so how do I get them to do their job correctly?
  • PingberPingber Member Posts: 9
    so ... after a few weeks, here's where we are ...

    HVAC firm finally agreed to come out again, this time, with the owner.  He agreed that my pipes do NOT go into the concrete and that there isn;t a leak.  He replaced the pump with the smae kind of pump that was on the furnace when we purchase it, a Taco.  He insisted that the spirovent was working, even thoughm when he took it apart it looked like it had come right out of the box, no "green" on the brass, etc, no evidence that anything had come through that nozzle in 3 years.  He also couldn;t blow air through the small nozzle.  Anyway, we now have incredible air int he downstairs loop of the house.  This loop has alot of ups and downs over doors, into ceilings, etc, so plenty of places where air can accumulate.  They are coming out again this week to replace the spirovent and re-bleed the system.  I don;t know what else to do at this point.
  • PingberPingber Member Posts: 9
    oh and one more thing

    HVAC did contact the pump company that was giving us problems ... the company said that they did have a few pumps that seemed to be gathering air around a check valve in the pump, then releasing that air when the water was heating up ... hmmmm ...
  • GordanGordan Member Posts: 891
    Caveat: this won't work if it's a compression tank

    It will only work with a diaphragm-style expansion tank. A compression tank would get water logged if it's not piped to the top of the air scoop.
  • PingberPingber Member Posts: 9
    and FINALLY, a solution

    Well finally, here's what happened.  They came again and replaced the pump with a Teco (sp?) that was the original pump on the unit.  That stopped the sound, but left an incredible amount of air in the system that they couldn;t seem to bleed out.  I had them return again and they replaced the spirovent which they said was faulty.  I reminded them that I told them that it hadn;t worked from the BEGINING (now 3 yeas)  As soon as they replaced it, it started doing its job and now all is quiet on the western front.  I think its time to find a new HVAC p[erson that's more responsive to what the customer is saying.  The only good thing about my current HVAC firm is that they are prompt and throughout this mess, they haven;t charged me.
  • icesailoricesailor Member Posts: 7,265
    Sounds in pipes:

    Don't be too hard on the HVAC company. This problem with cavitation is difficult to understand and difficult to overcome on occasions. If there is a lot of restriction in the piping system, it may set up the conditions for it to happen, It can also be the design of the impeller. All impellers are not equal.

    Nuclear submarines cavitate. Why not your impeller. A sub prop is the same as the prop on your outboard. I'm surprised that it didn't stop. I have a second floor zone that seems to bubble slightly when it first comes on in the AM when the clock thermostat starts up the zone. It goes away after that.
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