copper fin II with MP2 control, error code

[hvacpope]

large building with many WSHP, typical set up using couples of Lochinvar boilers to keep the loop around 80F, one of the boilers locked out on "Max delta T ERR", check the settings and the max delta is set at 50F, same in all 4 units, the pumps are running fine, besides water flow what else can cause the error code?

[doubleduece]

A bad sensor.

What is the delta T on the MP2 compared to the boiler display when the boiler is running?

What is the Delta T on the MP2 when the boiler is not running?

how many stages do each boiler have?

What is the delta P?

[hvacpope]

Its a four stages boiler, the delta T averages 7.4 degree per stage, I ran the boiler at full capacity and the delta did not exceeded 32 degrees, I also strapped thermistors to supply and return and compared my readings to the boilers sensors and they are dead on. I opened the bypass a turn and increased the max delta to 54, lets see whats happens Monday. I was thinking it was a post purge issue with the pump and boiler shutting down at the same time allowing for the delta to build. the problem happens over night only, the boiler runs fine during the day.

[doubleduece]

Your system should be piped primary/secondary, and I sure it is. When you say post purge, that usually means how long a comb. fan runs after the gas valve turns off. Im sure you mean how long the boiler(secondary pump runs after the boiler satisfies, it should be set for at least 5min. Also check the timing(MP2 uses timing to bring on the next stage) for stage up and extend it, double it, at night you have no load so maybe the boiler is staging to fast. Cavet, if your delta p is good timing doesnt matter, if your delta p is good you should hit your max delta p. It might also be a good idea to check your gas pressure leaving each gv to make sure you are not overfiring.

[hvacpope]

its a primary/secondary loop, the timing between stages is set at 4mn.