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  1. #1
    Join Date
    Jan 2013
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    Munchkin 140 making grinding noises when very cold outside.

    I have a munchkin 140 boiler that makes strange noises when it is below 0 outside. I think this is due to improper timing between the circulators and the boiler. I have a radiant heating system with three zones. When one zone calls for heat the zone circulator turns on. If the circulating water temp is not high enough the main circulator turns on, a few seconds later the blower turns on followed by the gas valve opening and the boiler flame igniting. The boiler commonly shuts the gas then reignites. When the circulating water temp reaches the set point the zone circulator continues to run, the main circulator turns off, a few seconds later the gas valve shuts extinguishing the burner flame and the blower goes into the purge cycle. When the circulating temp fall too far the cycle starts again from when the main circulator activates. The system has an outside temperature detector which raises the circulating water temp the lower the outside temp is. When the temp outside is below zero the system makes some grinding/knocking noises just before the boiler flame goes out (after the main circulator shuts off). I believe this is because the boiler temp shoots up in those couple seconds between when the main circulator shuts off and the flame shuts off. If the circulating temp is low enough the rise in temp isn't enough to make noises but if the circulating temp is high enough the boiler temp gets up very high and causes the noises. Does this sound like a valid theory and should I locate a technician to adjust this? Thanks.

  2. #2
    Join Date
    Jun 2007
    Minneapolis, MN
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    Your boiler is flashing to steam. This is the down side to low-mass heat exchangers used for high efficiency condensing boilers. Couple this with the fact that most boilers are grossly over-sized and zones are often designed with no regard to the minimum output of the boiler they are served by and you have a formula for failure. By all means find a contractor that specializes in condensing boilers (They all function essentially the same). You find them by calling and asking if the SELL them. If not, you will likely get a technician stuck in the last century.

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