Weil-McLain 97+ 155 - Short Cycling

skiereric

I recently purchased a home with a Weil-McLain 97+ 155. It is set up in two zones. One is DHW the other for the radiators.

As soon as I moved in I noticed an issue where the boiler would go in pre-purge, ignition, fan coil. Once lit, it would stay lit for 10 seconds and then post purge and repeat. No error messages. DHW was still producing enough heat for hot water and the short cycling kept the return line at around 80f, supply never got hotter than 100f with a target of 150f

I found this service bulletin which allowed me to use the lower setting as a temporary fix. I had a HVAC tech make the repair shortly after.

This seems to fix the problem and the house heated well all season.

Had the boiler serviced in August.

Fast forwards to today. First cold day. Set the thermostat to heat and the short cycling problem reappeared. The trick to lower to boiler setting now results in an Ignition Failure lockout. No error messages when using the correct 155 setting.

skiereric

skiereric

Update: this morning I went into "Manual Test Mode" and changed the "Force Rate" from Auto to High. The boiler updated normally until it reverted back to Auto.

neilc

is that heating circulator working ?

skiereric

Yes, the heating circulator is working. I know this because when I went into Manual Test Mode and changed the Force rate to high, the system was able to reach the target temperature.

What occurs in Auto is the boiler will fire for <10 seconds and then will go into post purge. This repeats indefinitely.