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Weil McClaine GV3 intermitnant lockout

Gene_3 Member Posts: 289
and not the pressure switch???? you may have a bad probe


  • Joe Annon
    Joe Annon Member Posts: 1

    This is a Weil McClaine GV 3 operating for 14 months with no problems. Over the phone with HO trouble shot to the point that chart said that there was leaking voltage from t-stats to boiler causing lockout. HO disconnected power to t-stats and boilr ran fine to heat side arm tanbk. When I got there and reconnected the transformer the boiler would go through to the pressure switch light which would come for a second or two then blink off then back on then off again then boler would start over for restart. I disconnected thepressure switch contacts and tested for continuity. Found that the switch would slowly close. Then I thought I would see what the reading would be when the pressure switch was connected. I pushed the probes in to the plug on the control module. It would start with open line then start closing but also with voltage causing the meter to complain about voltage. Now aftyer two times of this it stopped doing the voltage through meter and cycled about 10 times with no problems. I don't want to start throwing parts at the problem without knowing that there is a failed part.

    I am thinking that it is a pressure switch that is in the process of failing. but want to make sure customer is 110 miles away. And has been a very good customer.
    Joe Annon
  • GV Lockout

    Without a magnahelic it's impossible to properly troubleshoout a pressure switch. It's also important to know the make and break pressure of that switch. On startup there s/b 24 volts across the terminals of the switch and as the motor ramps up, the switch will make and display zero(unless you have a lead on common, then you'll see 24 on both terminals). As an aside, I have seen the contact points inside the molex plug on the circuit board open up and make poor contact with the male connector. It doesn't take much of a gap in the brass to screw up its conductivity. Look for a gap in the circular connector inside the molex plug.
  • Joe Annon_2
    Joe Annon_2 Member Posts: 11
    Pressure switch

    What i saw with the ohm meter was that the switch when closing was very slow to make complete contact but on opening at a very slow fan speed; almost stopped rotating; the switch opens cleanly going from closed to open circuit without time for the digital ohm meter to show the resisstance increasing. while closing it counts down to a closed switch.

  • Mr. Blonde
    Mr. Blonde Member Posts: 38

    If this is a series 1 or 2 gv then I would almost guarantee you that the heat exchanger is full of scale and plugged causing intermittent lock outs via the preassure switch.
  • Terry_14
    Terry_14 Member Posts: 209
    I agree with scale

    Experianced the same problem and ended up with a cold boiler a hose and a shop vac to catch the mess.

    The condensate trap on bottom had not been cleaned for ???? years and caused the condensate and scale.

    Proper cleanings have solved the issue.

    Good luck Terry
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