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Triangle Tube CC125 Condensing Boiler Short Cycling

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Hi,

I just want to thank everyone in advance for all your help. I bought a new home and it came with a Triangle Tube CC125 condensing boiler that was installed in 2013. It is a one loop system hooked up to one Grundfos UPS 15-58 pump. The system in question is on the first floor of a 2 family home. It is a quite small apartment, about 800-900 sq ft. in size. By my rough estimate, there is about 100 linear feet of radiator fins running through the apartment.

After reading and searching through this board, I think I am experiencing a short cycling problem. The heat curve is set at 120F minimum heat supply with upper limit set to 190F. The outdoor minimum temperature is set to 20F so anything less than that it should be running at 100% capacity. It is connected to a simple Honeywell programmable thermostat upstairs. The problem I am experiencing is that the heater would fire-up for 5 to 10 minutes before shutting down and going back to Fan pre-purge or post-purge cycle. I am a novice at this but I think it is going back into standby because the return water has reached the preset temperature set at the machine so it's shutting off.

In terms of the display on the machine, it shows stage 1 (pre-purge or post purge cycle) with the water temperature reading. Once the water temperature drops to around 120F, it would change to stage 2 (ignition sequence) for 1-2 seconds before going to stage 3 (Burner ON for space heating) and water temperature would reach 185-190F fairly quickly. It would stay at stage 3 for 5 - 10 minutes before going back to stage 1. I know the Thermostat is still calling for heat because if the room has reached the set temperature, the display would change to XXXP with no display on the Stage indicator. I have tried setting the pump to Low, Med and High but it still seem to be firing up for only a short time.

Is there anything I can do to fix this? Also, would a lower pump speed setting be better as to allow the heat to dissipate before returning back to boiler?

Thanks again!

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