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Vaillant boiler pressure

Discussion in 'Electronic Repair' started by M.Joshi, Jun 18, 2007.

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  1. M.Joshi

    M.Joshi Guest

    Hello,

    Every two weeks, the pressure gauge on our Vaillant ecoTech Plus keep
    going down to zero and I have to top up the radiators with more water.

    Our plumber has tightened a suspect leaking towel radiator but th
    pressure still seems to gradually drop over two weeks.

    He is going to use Sentinel Leak Fix.

    I am not convinced that using this product will completely solve th
    problem.

    Is there anything else that can be checked which may cause the loss o
    pressure
     
  2. Baron

    Baron Guest

    M.Joshi inscribed thus:
    I'm not a plumber but if you are loosing water from a sealed system it
    has got to be escaping from somewhere. Any joint, soldered,
    compression or otherwise is a potential source of escape. You should
    carefully inspect every pipe, starting from one end of the system and
    working your way round each radiator. Don't forget to check any taps,
    drains, or bleeds! Any sign of sweat or moisture could indicate your
    leak! The problem is that moisture very quickly evaporates,
    particularly if the environment is warm.

    Murphy dictates that any leak will be in the hardest place to get
    at !! Good Luck.
     
  3. James Sweet

    James Sweet Guest


    Can you pressurize the system with air while cold? I've used that trick to
    find leaks in automotive cooling systems. I haven't seen radiators used to
    heat a house since a few built back in the 1950s but the systems are usually
    pretty simple.
     
  4. m kinsler

    m kinsler Guest

    Can you pressurize the system with air while cold? I've used that trick to
    That's what I'd do. Figure out how to connect a tire valve into one
    of the system's air vents. Then pressurize the whole thing with a
    bicycle pump to maybe fifty psi and then go over every joint with
    liquid soap and look for bubbles. If you can avoid using the
    plumber's sealant stuff, it would probably be better just on general
    principles.

    It occurs to me that this is the sort of thing I ought to do whenever
    I do an extensive plumbing job around here: insinuate a Schrader tire
    valve into the water system somewhere and whenever I think
    everything's going to be just swell, pressurize it to a good hundred
    psi with the air compressor and see if it actually is.

    M Kinsler
     
  5. Guest

    Lots of things going on here, and a lot more information is required
    in order to diagnose this properly.

    How old is the system for one. Not the boiler, but the entire system.

    a) What kind of system is this - One or Two pipe?
    b) Copper or Iron?
    c) Are there any direct copper-to-iron connections?
    d) What kind of expansion tank do you have?
    e) And have you verified the pressure in it if it is a bladder tank,
    or have you drained it recently if it is a water tank?
    f) Do you have automatic bleeder valves? If so what kind?
    g) Do you have an automatic fill valve?
    h) One, two, three-or-more story application?
    i) How recent was the boiler installation?
    j) How long has this been going on?
    k) If this is a vintage system originally, was it sized for gravity or
    pump circulator?
    l) And how big (how many radiators) is the system overall?

    In general, how do you like this little boiler? As I understand it, it
    is a gas-fired, stainless steel, wall-hung condensing boiler?

    There does happen to be a recall on some Vaillant boilers, have you
    checked that? That may be the explanation right there.

    DO NOT pressurize the system with air, and most especially DO NOT
    pressurize to anything near 50#. First you will blow out the TPR valve
    on the boiler, second, you stand to blow out the gaskets in the heat-
    exchanger.

    If the system is two-pipe, black iron, and sized for a circulator, the
    leaks will be at-or-around any new installations you may have made or
    had made. This could include the boiler, the towel-warmer radiator or
    any other radiators you have installed. It is also possible, but
    unlikely that recent installations disturbed an existing joint, or a
    knuckle was disturbed for alignment purposes somewhere within the old
    piping. This should show pretty obviously.

    It is also entirely possible that the system has not been bled
    properly (assuming you have automatic bleeders) and what you are
    observing is simply the bleeding taking its natural course. It could
    also be that you have an undersized expansion tank (a very common
    problem if retrofit).

    If this is a recently installed all-copper, sweat-connection system,
    look for inadequate expansion loops. That can crack a joint or fitting
    *just* enough for a tiny leak visible only under pressure.

    There are just too many variables to diagnose a problem without
    additional information.

    Lastly, Miracle-Shyte-Glyte-Leakstop is NOT what you want to install
    in any system, especially a high-efficiency copper-based (if that is
    what this is) system. It will greatly degrade the heat-exchange
    equations going and coming and is altogether a bad idea. Find the
    cause of the pressure drop and fix it.

    Peter Wieck
    Wyncote, PA
     
  6. m kinsler

    m kinsler Guest

    DO NOT pressurize the system with air, and most especially DO NOT
    Whoops. In that case, I gave bad advice. I'd assumed that this was
    like any other plumbing system and would withstand city water
    pressure.

    M Kinsler
     
  7. Guest

    It happens. Few individuals understand radiant heat anymore. It is a
    wonderful system designed properly and can be very efficient as it
    puts heat where it does the most good. But, sadly, it does not support
    central AC, a major drawback these days.

    Peter Wieck
    Wyncote, PA
     
  8. Baron

    Baron Guest

    m kinsler inscribed thus:
    Actually, thinking about it, that is a good idea ! The system should
    be able to withstand 50 - 100 psi without too much stress. The soap
    water trick should work well.
     
  9. James Sweet

    James Sweet Guest


    Agreed that 50 PSI is way too much, but I don't see a problem with
    pressurizing it. When I test automotive cooling systems I pump them up to
    about 3 PSI with a bicycle pump, I do this on top of the water already in
    there, at which point it will usually drip from the leaky part instead of
    coming out as invisible steam.
     
  10. Guest


    Do you know about Hydronic heating systems? Any domestic system that I
    know will blow (at least) several gaskets if pressurized to 50#,
    possibly more if done so 'dry'. I guess you could tie down or cap the
    TPR valve and take your chances, but the other potential is that many
    more joints might fail if it is a threaded iron system.

    Keep in mind that older systems required pressure only enough to bring
    water to the highest point in the system, cold. Normal expansion would
    then increase the pressure under operating conditions with water at
    anything from ~140F to 180F (60C - 83C) depending on the type of
    system and radiator/heat-exchanger design. So, the system would be
    provided with an expansion-tank. Some were open and at the top of the
    system, some were gravity and at the bottom. Today, pre-pressurized
    bladder tanks are used such that they will maintain near-0 content
    cold but accept expansion without a significant increase in system
    pressure.

    We run a system with a 12-meter rise at about 15 psi (1.03bar). When
    at operating temperature (140F/60C) pressure increases only to 18psi
    (1.24bar), not much considering it is a black-iron two-pipe system.
    Just for the sake of clarity, a "two-pipe" system means that each
    radiator is the same virtual distance from the boiler, and so each
    radiator heats up at the same rate and at the same time. It is easy to
    conceive: Draw two parallel lines, label one "supply and the other
    "return". The individual radiators cross from the one side to the
    other. Now, draw a line from the SUPPLY side on the right to a box.
    And from the RETURN SIDE on the left to the same box. Label the box
    "Boiler". You can see that the radiator closest on the supply side is
    furthest on the return side, and vice-versa. The one in the middle is
    equi-distant. That is how it works. Our TPR valve is set for 30psi/
    200F. Some margin, but not a huge amount nor would we want it so.

    Most modern installed systems are simple loops. The radiator closest
    to the supply heats first. The guy last in line gets short shrift.

    Peter Wieck
    Wyncote, PA
     
  11. Baron

    Baron Guest

    inscribed thus:
    Thankyou for your notes. I did say up front that I was not a plumber!
    However I do understand what you are saying and appreciate it. I can
    see why pressurising a system in the way described is not a good
    idea. I withdraw my comment unreservedly.
     
  12. Guest


    As I have written before, hydronic systems are nearly a lost art in
    domestic applications. I have installed two in my time and repaired
    MANY, and I am perhaps the youngest person (at 55) that I know not a
    professional plumber or engineer that has any clue about their general
    operation. But I have lived in two houses with such systems, both over
    100 years old, both retro-fitted from either stove/fireplace or coal-
    fired octopus systems to hydronics in the '30s. Self-defense has made
    me quite familiar with their vagaries.

    Peter Wieck
    Wyncote, PA
     
  13. Rudge

    Rudge Guest

    Are you sure that water is not leaking through the pressure release valve?
    It sometimes evaporates and leaves no evidence.
    Can you temporarily connect a hose and a container to catch any water
    leaking from the pressure release valve pipe which exits outside the
    buliding.

    Rudge.
     
  14. M.Joshi

    M.Joshi Guest

    Thank you all for your replies.

    Firstly, in response to your first post Peter:

    "How old is the system for one. Not the boiler, but the entir
    system."
    Originally we had a gravity fed system fitted about 30 years ago with
    cold water tank in the loft and a hot water storage tank below. Thi
    system was recently replaced by a Megaflo tank and Vaillant condensin
    combi boiler. As this is a pressurised system the cold water storag
    tanks were no longer requried. We replaced some of the radiators wit
    newer ones and additional ones were added including a towel radiator.

    a) What kind of system is this - One or Two pipe?
    I believe two pipe - Separate water and heating pipes.
    b) Copper or Iron?
    Copper
    c) Are there any direct copper-to-iron connections?
    I don't think so?
    d) What kind of expansion tank do you have?
    None
    e) And have you verified the pressure in it if it is a bladder tank,
    or have you drained it recently if it is a water tank?
    N/A
    f) Do you have automatic bleeder valves? If so what kind?
    Manual bleeder valves on the radiators. An automatic bleeder valve o
    the Megaflo tank I believe?
    g) Do you have an automatic fill valve?
    Manual filling loop to pressurise the system
    h) One, two, three-or-more story application?
    Two storey
    i) How recent was the boiler installation?
    A few months
    j) How long has this been going on?
    SInce it was installed
    k) If this is a vintage system originally, was it sized for gravity or
    pump circulator?
    Gravity - pump
    l) And how big (how many radiators) is the system overall?
    10
    In general, how do you like this little boiler? As I understand it, it
    is a gas-fired, stainless steel, wall-hung condensing boiler?
    It is supposed to be a good reliable boiler. Hard to comment o
    performance as we have only had it installed for a few months.

    "Rudge, in answer to your question:
    Are you sure that water is not leaking through the pressure releas
    valve?
    It sometimes evaporates and leaves no evidence.
    Can you temporarily connect a hose and a container to catch any water
    leaking from the pressure release valve pipe which exits outside the
    buliding.

    Rudge."


    I don't think any of the radiator bleeders are leaking. The only leak
    spotted was on the towel radiator valve which was tightened by th
    plumber.

    I have noticed a stream of water escaping from the flue while th
    boiler is operating which I find rather strange?

    Thanks
     
  15. I have also seen the PRV fail. The spring weakens slightly. It holds the
    pressure when cold and topped up even to 3 bar when we tested it but weeps
    slightly in service so the pressure drops slowly over several days when in
    use.

    HTH
     
  16. Guest

    A couple of things first:

    a) Condensing boilers exhause either 'steam' or steam with a small
    stream of water. That is their nature and not of concern. The chemical
    reaction is 2CH4 + 3O2 = 2CO2 + 4H2O or, lots of water.

    b) "Two-Pipe" system relates to how the radiators are fed. A loop-
    system puts the radiators on a loop such that the radiator nearest the
    boiler sees hot water first, then the next and the next until the
    entire system equalizes, excepting that the last radiator in the line
    is always coolest. A "Two-Pipe" system sets up parallel supply and
    return lines such that all the radiators "see" the boiler at the same
    distance. The first radiator on the supply side is the last on the
    return side, the last on the supply-side is first on the return side.
    This system heats all the radiators at the same rate simultaneously
    and is the most efficient except that it requires 50% more pipe and
    very careful planning/engineering as compared to a loop system.

    c) I am gathering that your system provides domestic hot water as well
    as heating water, and so here in the US, we would call it a "summer/
    winter hook-up". That is quite an elegant use of these boilers, about
    the only thing more efficient than such a system would be some of the
    tankless instant-hot water-systems.

    But, cutting to the chase, somewhere, some how, there *must* be an
    expansion-tank. Your Megaflo tank is simply a heat-exchanger loop from
    the boiler to a domestic hot water storage tank, and most emphatically
    *NOT* an expansion tank. The bleeder is for the domestic water side,
    not the central heat side.

    If you do not have an expansion-tank within the system, may I gather
    that you have not yet used it for heat in the winter? Because when you
    do, you will absolutely blow off the TPR valve, which if not vented
    outside will be a hot, smelly mess on top of which you risk boiling
    out your system otherwise. And, this is absolutely the source of your
    pressure drop. The system is over-pressurizing each cycle and either
    venting through the valve slowly or at some hidden fitting.

    Please check again for an expansion tank. With only ten radiators, it
    may be as small as a football (soccer ball, for the US) and hidden in
    some corner somewhere. If you have one, make sure that it is properly
    pressurized and/or properly drained (if from the old system). If it is
    a bladder-tank there will be a Schrader-valve on it that you may check
    with a tire pressure gauge and charge with a bicycle tire pump. For 2
    stories, charge it to about 12psi... and MAKE SURE it holds at that
    pressure.

    An all-copper system only 30 years old would not be gravity. Gravity
    systems use VERY fat pipe on the return side relative to the supply
    side and special valves such that expanding (freshly heated) water
    pushes through the valve causing flow. They are typically designed
    against standing-pilot systems with millivolt-pile thermostats run
    from electricity generated by the pilot through a thermocouple. These
    were designed for areas where mains power either did not exist or was
    unreliable. Very elegant, very simple. Not terribly efficient by
    modern standards.

    Peter Wieck
    Wyncote, PA
     
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