Weil McClaine GV3 intermitnant lockout

Gene_3

and not the pressure switch???? you may have a bad probe

Joe Annon

Lockout

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

Darin in Michigan

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

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.

Joe

Mr. Blonde

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

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