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Ghost flow

Greg Maxwell
Greg Maxwell Member Posts: 212
We have a customer that has a coil boiler, 1-1" split loop, and 1-3/4 loop. The system has run fine for years. The pressure is at 20psi, 180 high limit. They just installed a commercial dishwasher, and when the dishwasher runs, of course the boiler fires, then one side of the 1" split gravity flows up to a certain point on the loop, then stops. The returns are cold, no pumps running. There is a check on both zones, and the check on the 1" loop is before the split. We have had everone here looking at his drawing, but we are scratching our heads. He even took out the flow check, and replaced it with a spring check.

Any ideas?


  • icesailor
    icesailor Member Posts: 7,265
    Ghost Flow:

    The "coil" is to an indirect? The two zones are for heating?

    If you are running a boiler for space heating and using part of it for heating domestic potable water, and it is a cold start boiler, you can have a lot of thermal expansion with a cold start. If the Extrol type tank is on the supply and it is accepting the thermal expansion of the water, it is flowing to the expansion tank and you should get some flow in the 1 1/4" circuit. In MY opinion. If the expansion tank isn't big enough, I've seen this flow before. If you are trying to get 180 degree domestic hot water to a dishwasher, you have a big heat load on the boiler and the expansion tank may need to be re sized
  • Greg Maxwell
    Greg Maxwell Member Posts: 212
    Ghost Flow

    There is no indirect water heater. It is running 160lo limit 180 hi limit. The boiler pressure is at 20psi
  • Paul Fredricks_3
    Paul Fredricks_3 Member Posts: 1,557

    Don't know why it started now, but when we had ghost flow issues we'd put a swing check at the end of each loop on the split zone. That always solved it for us.
  • billtwocase
    billtwocase Member Posts: 2,385
    pics will help

    but I would say bad 1" flow check valve. Where is the expansion tank on the system, and why 20 PSI?
  • Techman
    Techman Member Posts: 2,144

    Having a check valve added to the return has stopped any ghost flows for us.
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