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Pressure Relief undersized on European Boilers?

DD_5
DD_5 Member Posts: 36
in THE MAIN WALL
I recently trouble shot a LAARS wall hung combi boiler. The pressure relief on the radiant heat side kept leaking through. I replaced the original 30 PSI valve with another...and it happened again. I replaced that one...same problem. The gauge on the boiler seemed to be working just fine, it's an analog gauge. The boiler manual calls out a 30 PSI pressure relief.

Here's the rub....The gauge indicates blow off at 3 bar. That's 43.51 PSI ! Even if I fill the unit to a recommended 1.5, that's 21.75 and if the heat brings it up near 2, that's 29 PSI. So I think that most 30 PSI valves will act like the ones I put in and leak slightly as the pressure approaches 2 bar.

Question: Since the blow off set point on the boiler gauge is a whopping 3 bar...shouldn't I be installing a 50 PSI relief valve? Is this 30 PSI assumption a sloppy conversion error on the part of American distributors?

Sorry my faithful country tis of thee but there are a heck of a lot more salesmen these days than engineers...

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Comments

  • icesailor
    icesailor Member Posts: 7,265
    Undersized?

    Maybe you need a larger expansion tank than the one installed? Those symptoms sound like the problem. Or the tank is mis-located.
  • Jim Godbout
    Jim Godbout Member Posts: 49
    Expansion tank

    Definitely internal expansion tank they are small and usually fail after a few years of service

    Easier to add one then replace

    Good luck

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  • Jeremy_14
    Jeremy_14 Member Posts: 34
    Radiant side?

    On most heating systems there is one pressure relief valve that is designed to protect the boiler from any water pressure higher than 30 psi. I am translating your question to mean that on this heating system there is more then one relief valve installed that will release at 30 psi or above, and the one on the radiant side is failing. What do you mean by the radiant side? Is the radiant heat piping tied directly with the boiler or seperate from the boiler piping, with heat being transferred through a water to water brazed plate heat exchanger, or water heater? Often a relief valve fails because the expansion tank has failed, or maybe in this case, there was no expansion tank on the radiant side.
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