Navien NCB-240 Internal Circulator Variable or Single Speed

axeyal

I'm trying to balance my Primary / Secondary flow and would like to understand if the internal circulator in the Navien NCB-240 runs on a single speed or does it have more than one speed to modulate with the firing rate?

Zman

It's probably single speed. Do you know what model the circ is?

axeyal

Thanks Zman,
The model number is 30012768A Circulation Pump.

motoguy128

Its 3 fixed speeds manually adjustable only. Similar to a grundfos 15-58 3 speed. Its flow rate is only good enough for about 7 Gpm max I think. So the flow is about 4-7gpm

motoguy128

That’s one huge limitation of a combi. Depending on desired supply temp, the capacity is limited by primary loop flow. So if you have a bigger cast iron system and have lets say 14gpm on the secondary, if 150 gives you let’s say 15f delta t across the system and it comes back at 135f, you have to supply 165f water. Not a big deal but something to keep in mind.

axeyal

motoguy128 said:

Its 3 fixed speeds manually adjustable only. Similar to a grundfos 15-58 3 speed. Its flow rate is only good enough for about 7 Gpm max I think. So the flow is about 4-7gpm

The installation manual does not mention an adjustment on the circulator. That makes me believe it is a single speed. Do you have any documentation showing otherwise?

axeyal

I read somewhere in this forum before that the flow rate of the circulator is 5gpm. I am getting lower water temperature reading at the secondary loop supply than the primary loop supply temperature on the boiler. This makes me think that I need to reduce the flow in the secondary loop so there is less mixing of return water across the closely spaced Ts