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Intermittent lockout problem with 20 yr old W-M Gas Boiler GV4, Series 2
I have a 20 yr. old Weil-McLain GV4 Series 2 natural gas boiler with the UTC 1013-100 control module & White-Rodgers 36C98 gas valve. Also have a Weil-McLain water heat exchanger & Wirsbo floor heating with 3 zones. . I am having problems with intermittent lockout. Turn off power & boiler fires normally again. May go several days to a month then lockout again. Have followed W-M's trouble shooting guide & checked differential pressure at air pressure switch using a Dwyer Mark II #25 manometer. The reading was 2.1" W.C. at start of purge then dropped to about 1.7" W.C. during normal operation. Have about 30' of vent/intake piping. Original was PVC & was replaced on recall about 2 or 3 yrs. ago. Have checked all wiring connections, have 24VAC at air pressure switch, 129 VAC at main line connection at control module. Blower motor is rated 1.0 A pulls 3.1 A startup then drops to 0.99-1.02 during run. Replaced the igniter in October because of intermittent lockout but did not solve problem. Checked with magnifier all solder joints on back of control board. Could not see any cracks or problems. Also ck'ed Grundfos circulation pump, rated 0.74 A pulling 0.7+-. Suggestions??
Forgot to mention when the boiler locks out the green power light is on steady, the gas valve light is blinking red. Purge & ignitor lights are not on.