Triangle Tube CC125 Condensing Boiler Short Cycling

petec88

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!

NY_Rob

Is the Triangle Tube CC125 supplying just the 1st floor heating loop with 100' total fin tube?

The 2nd floor has it's own boiler?

kcopp

Is it possible that there is a draw for hot water in this time?

petec88

The Direct Hot Water has not been setup so the boiler is just being used for heating only. The boiler is just supplying 1st floor. 2nd floor has it's own boiler which has a much longer loop (around 200') and that one is working fine for now.

kcopp

So this boiler has 1 circ pump for the boiler and another to go out to the baseboard?
I would agree about the oversizing if this boiler will always be used to do Heat only. Its not per se oversized if the hot water part of it is used. You will need all 125K btu to get the proper hot water output.

petec88

Hattersday, thank you for your comment and suggestion. In regards to your suggestion on the P parameter for the "anti-cycling period during CH operation," would it be able to make a significant different in getting the temperature of the house up? right now, the issue the system is cooling down for about 10 minutes after firing up for 5 minutes. The problem is that the house temperature is not getting to the thermostat set temperature before the limit kicks in. I think what I want to do is somehow get the boiler to fire longer so that the temperature can reach temperature set on the T-stat. Is there other settings I should adjust. Will adjusting the pump speed somehow allow me to dissipate more heat before the system shuts down? (It is currently set on low)

Kcopp, yes the boiler has 1 circ pump on the return side to pump the water through the system. There is no pump on the supply side as the tube just goes out to the baseboards. Are you saying that if I hook up the hot water feed that it might be able to solve this problem with oversizing and short cycling?

Gordy

As @Hatterasguy pointed out the boiler is oversized by a considerable margin, and the low end modulation is not near low enough to compensate for the oversizing. There is no way of getting around this. A properly sized buffer tank helps, but is not a 100% fix in mild temps.

kcopp

Can you post a picture of the install please... ?

petec88

@kcopp I won't be home till late tonight. I'll try to post something for you tomorrow. I'll take a picture of the boiler and the supply & return lines with the pump.

smithfan

Can't you just get rid of your second floor boiler, and tie in the Triangle Tube to the whole house? It's way oversized, the 200 ft of emitters on the second floor could essentially act as your buffer tank.

petec88

Thank you @Hatterasguy I went to the boiler and the parameter "P" is showing as a temperature range (between 33 - 59) and not a time range. I looked up the manual and it gives a time range for P parameter as well so I'm not sure what that setting is showing on the boiler now.

Gordy

The 200 feet of emitter is another post, and one loop to much for one loop.

petec88

So spoke with Tech support at TT and they claim that it's nothing wrong with the boiler and it's more a problem with the water flow through the piping it sounded like to them. They also said that I should have a primary/secondary loop in the system.

Now the other boiler I have in my other post does have a primary and secondary loop but this one doesn't. Please see picture attached. Is a primary/secondary loop necessary and how will that prevent short-cycling? Also, they mentioned that I need a pump on the primary loop (the short run between supply and return on the boiler). Is that also really necessary? I might go and put the primary loop back in, if so, do I really need to attach a pump?

Sorry for the angle of the picture, its a tight space. The pump on the left side of the photo belongs to the other burner not this one. This one also only has one Grundfos USP 15-58fc pump on the return.

Gordy

From the manual.