L7224 Thermal Purge settings

Robert_H

Servicing a Dunkirk DK4EXA075, fired at spec, 60-60B at 150psi. It is a direct vent system.

It is supplying the first floor of a three story house that the first floor was cut out as a rental and of course is oversized for the space. Cold start with no DHW

I service another boiler in the same basement so I have heard it cycle quite a bit. I don't think I have ever heard it run for more than three min, usually more like two min. The off cycles are usually 10 to 20 min. and the boiler doesn't cool off much in that time.

CA

MFR	Dunkirk
model	DK4EXA075
nozzle	60-60B
Pump Pres	150
Firing Rate	= 0.73
Tstack	345
O2	4.3
CO	48
EFF	86
ExAir	24
CO2	12.48
AT	46
Net Stack	299

This was at zero smoke, I forgot to save the data at Zero-1.5 % CO2 🙄. I'm sure at -1.5 the stack temp was higher but not by much.

High Limit is at 180, High Limit diff is maxed out at 20, which has no effect because the call for heat is usually satisficed before hitting high limit.

If I understand the manual for the L7224 , Anti Short Cycle (ASC) only effects the off cycle which is not the issue here. From what I have read here on HH Thermal Purge should be useful in this situation. If so, what would be good strarting settings for Thermal Purge Temperature Limit (tPL) and Thermal Purge Time Delay (tPt)?

Thanks!