Weil-McLain gas boiler short cycling, weak flame signal and lockouts

The boiler is a 1991 Weil-McLain  HE-3, induced draft gas hot water boiler for

single zone baseboard hot water heat.  It

uses a White-Rogers 50E47-842 HSI Control. Igniter and Flame Sensor are

replaced every heating season. Gas valve and control board were new 1 year ago,

as were several other parts. New gas line from street, and meter, installed 4

years ago, with line gas pressure delivered to boiler satisfactorily resolved to

5" - 5.5 WC, verified by gas company tech, HVAC tech and myself.It is installed in the dug-out portion of the house crawlspace.

The dug-out portion has concrete block retaining walls, full concrete floor, and

has been fully encapsulated. Ventilation is sufficient, and RH is 30 - 50% from

fall to spring.





 House is a rental unit located 30 miles away from our

residence, making accurate reporting and observation of problem occurrence, and

servicing challenging.





 During recent years (past 5) there have been consistent problems

with the "locking out", and shutting down. Many parts replacements

have occurred, including igniters and flame sensors, gas valve, transformers

and HSI control boards. Replacing parts usually results in a temporary fix, but

the lockout problems recur at some (variable) time later. There does not seem

to be any correlation between air temperature or conditions (rain / snow /

clear) and boiler performance.   





 Just experienced another lockout (flashing red light on the

HSI control), which somehow seems to have resolved itself for the moment, but I

am on my annual quest for a working boiler, and am turning here for assistance.





 Documentation is: Day 1: 0800





Tenant texts to advise of no heat that morning. He said that

heat had been fine previously. Stated that he had turned heat down the night

before, and when he turned it back up in the morning, it did not come one. Travelled

to site, reset the system by turning power off / on. Unit immediately fired up,

and completed ignition sequence. Observed rapid-flashing green light (weak flame)

for about 30 seconds, then solid green, indicating satisfactory flame. Cycling

time is about 3-4 minutes, raising water temperature from to 160 degrees (per

temp / pressure gauge). Drop to 140 degrees starts cycle again. Cycling, hot

water generation and heating continued for 2 hours of observation. Cycling was

always in 3-4 minute range. Weak flame signal appeared on each cycling. There

were two (2) failed 1st ignition attempts at 79 minutes and 98 minutes, but

both recovered on second attempt. Duration of weak flame signal increased to

about 50 seconds starting with first ignition failure, and continued for rest

of observation, 122 minutes. Observation and presence ended, since boiler was

firing and house heating.





2000 hours:  Tenant

returned home from work, reported house was cold, no heat and all pipes were

cold. Asked him to go to boiler, and observe and report while resetting. Walked

him through the process, advising what to do / look for. Boiler fired

immediately on reset, and he reported that HSI control idiot light was

immediately SOLID green (no flashing). Asked him to stay for several cycles,

and cycling was just as short as earlier; consistent immediate solid green light

at ignition for each of four (4) observed cycles.





 Day 2: 1300 hours. Checked residence: Toasty warm at 70

degrees; all pipes hot. Checked boiler: output pipe so hot you could not touch

(must have just finished cycle). Waited 45 minutes, but no further cycling

(tight little house!).





 To start, I need to resolve the short cycling, weak flame

signal and lockouts.





 I have some thoughts, but would appreciate questions, comments

and recommendations to start the discussion.