Mike Bernardo
New Member
Our 4 year-old Navien NCB-240 (propane) has been problematic for most of its life. Many parts have been replaced and is currently acting up again.
I was at my wits end and about to replace it with a different manufacturer, but as I learn more about mod/cons I'm starting to think maybe our heating system is not designed correctly and/or the 240 is oversized. My hunch is that this is at least partly to blame for the equipment failures we've been seeing.
Hoping I can get some advice from the group here on how to adjust or replace our system. Our Navien-certified contractors have been good at replacing parts, but lack advice on system design. (Recommendations for good hydronic system contractors in New England also welcome.)
Our setup:
Late 80s ~3000sqft 2-story "Acorn/Deck" style home in MA. Lots of big windows in main living area.
1st floor Main zone:
Living, Dining, Kitchen, Kids room
Baseboard: Mix of 40.5' of Runtal UF-2 and 28' of fin-tube baseboard
Mitsubishi MSZ-GE18NA-8 in Living/Dining
1st floor Master BR zone:
Master BR, Master Bath
14' Runtal UF-2 in BR, 6' in Bath
Mitsubishi MSZ-GE09NA-8 in BR
2nd floor zone:
2 bedroom, 1 bath
1 zone baseboard: Mix of 4' Runtal UF-2 and 37' of fin-tube baseboard
Mitsubishi MSZ-GE06NA-8 in each Bedroom
Basement zone:
Partially finished, almost entirely under grade (~550sqft)
1 zone 20' fin-tube baseboard
No outdoor sensor on the Navien. As far as I know, it has been set to 180 supply temp the entire time.
The Navien is currently occasionally throwing error E109 (air flow related error). Techs have replaced the fan, venturis, and ECB. Still E109. Latest advice from Navien tech support is to replace the air flow sensor and entire wiring harness. I have not done this yet as I'm usually able to get the unit to re-start by unplugging it for a bit and re-plug it back in. At this point I'm hesitant to throw more money at this unit.
My guess is that our use pattern on the Basement zone is the main culprit for the Navien breakdowns. It is a home office for me, so during the day it is usually the only zone operating. While working, I either turn down the 1st floor thermostat or turn on the Mitsu in the living room which keeps most of the 1st floor at temp.
When running Basement zone only, I have noticed it short-cycles the Navien like crazy. Once the fin-tubes are heated up, there is practically no temperature delta. Water goes out at 165 and comes back at 164/165. During heat calls on this zone, the Navien starts up and burns for 3-4 seconds and immediately shuts off. It waits the 3-minute cycle time and starts again, continuously. I have tried turning the zone circulation pump to it's slowest setting but that seems to have zero effect on temp delta. Mentioning this to the boiler techs a couple of times, they just shrug it off as "normal". Am I correct to assume this is catastrophic for the boiler to run this way for several hours a day?
The Navien seems to run the 1st floor pretty well. For example, today it's about 30-40F outdoors. I have set the supply temp to 170 and the Navien has spent a several hour-long burn getting it to 70F. Steady temp delta of 167->156F
2nd floor baseboard zones almost never used. Mitsus do a good job keeping the 2nd floor at temp on their own. Similarly, baseboard in Master BR zone almost never used.
How would you improve the current setup? I see a few options:
1.) Replace the Navien with a different combi manufacturer. My contractor suggested a Lochinvar or HTP.
Without adjustments to the Basement zone, this seems like a costly+bad idea and likely to cause the same short-cycling problem I have now.
2.) Improve the radiation of the Basement zone.
The Navien is clearly oversized for running this zone in isolation. Would going to bigger/more radiators help? My thought was to replace the 2 10' runs of fin-tube with bigger runtals (maybe UF-4 which is 930 BTUH/ft)
https://runtalnorthamerica.com/residential_radiators/baseboard_uf.html
3.) Change zone usage pattern and setbacks:
Currently we have Nest thermostats keeping the house at 68-70 while occupied and going down to 65 during the night and when we are away. We could add the outdoor kit to the Navien and try to move to a constant low-supply temp setup. This way, the basement has less of a chance of running in isolation since the 1st floor zone would be running more often. My concern is that this will increase fuel usage? It also negates the use of the Mitsus for heat?
4.) Move to something other than a mod/con boiler:
What are my options here? Clearly this will be costly, but perhaps makes sense if this mod/con is a lemon and/or the wrong type of boiler for my setup.
Other ideas? Thanks!
Mike
I was at my wits end and about to replace it with a different manufacturer, but as I learn more about mod/cons I'm starting to think maybe our heating system is not designed correctly and/or the 240 is oversized. My hunch is that this is at least partly to blame for the equipment failures we've been seeing.
Hoping I can get some advice from the group here on how to adjust or replace our system. Our Navien-certified contractors have been good at replacing parts, but lack advice on system design. (Recommendations for good hydronic system contractors in New England also welcome.)
Our setup:
Late 80s ~3000sqft 2-story "Acorn/Deck" style home in MA. Lots of big windows in main living area.
1st floor Main zone:
Living, Dining, Kitchen, Kids room
Baseboard: Mix of 40.5' of Runtal UF-2 and 28' of fin-tube baseboard
Mitsubishi MSZ-GE18NA-8 in Living/Dining
1st floor Master BR zone:
Master BR, Master Bath
14' Runtal UF-2 in BR, 6' in Bath
Mitsubishi MSZ-GE09NA-8 in BR
2nd floor zone:
2 bedroom, 1 bath
1 zone baseboard: Mix of 4' Runtal UF-2 and 37' of fin-tube baseboard
Mitsubishi MSZ-GE06NA-8 in each Bedroom
Basement zone:
Partially finished, almost entirely under grade (~550sqft)
1 zone 20' fin-tube baseboard
No outdoor sensor on the Navien. As far as I know, it has been set to 180 supply temp the entire time.
The Navien is currently occasionally throwing error E109 (air flow related error). Techs have replaced the fan, venturis, and ECB. Still E109. Latest advice from Navien tech support is to replace the air flow sensor and entire wiring harness. I have not done this yet as I'm usually able to get the unit to re-start by unplugging it for a bit and re-plug it back in. At this point I'm hesitant to throw more money at this unit.
My guess is that our use pattern on the Basement zone is the main culprit for the Navien breakdowns. It is a home office for me, so during the day it is usually the only zone operating. While working, I either turn down the 1st floor thermostat or turn on the Mitsu in the living room which keeps most of the 1st floor at temp.
When running Basement zone only, I have noticed it short-cycles the Navien like crazy. Once the fin-tubes are heated up, there is practically no temperature delta. Water goes out at 165 and comes back at 164/165. During heat calls on this zone, the Navien starts up and burns for 3-4 seconds and immediately shuts off. It waits the 3-minute cycle time and starts again, continuously. I have tried turning the zone circulation pump to it's slowest setting but that seems to have zero effect on temp delta. Mentioning this to the boiler techs a couple of times, they just shrug it off as "normal". Am I correct to assume this is catastrophic for the boiler to run this way for several hours a day?
The Navien seems to run the 1st floor pretty well. For example, today it's about 30-40F outdoors. I have set the supply temp to 170 and the Navien has spent a several hour-long burn getting it to 70F. Steady temp delta of 167->156F
2nd floor baseboard zones almost never used. Mitsus do a good job keeping the 2nd floor at temp on their own. Similarly, baseboard in Master BR zone almost never used.
How would you improve the current setup? I see a few options:
1.) Replace the Navien with a different combi manufacturer. My contractor suggested a Lochinvar or HTP.
Without adjustments to the Basement zone, this seems like a costly+bad idea and likely to cause the same short-cycling problem I have now.
2.) Improve the radiation of the Basement zone.
The Navien is clearly oversized for running this zone in isolation. Would going to bigger/more radiators help? My thought was to replace the 2 10' runs of fin-tube with bigger runtals (maybe UF-4 which is 930 BTUH/ft)
https://runtalnorthamerica.com/residential_radiators/baseboard_uf.html
3.) Change zone usage pattern and setbacks:
Currently we have Nest thermostats keeping the house at 68-70 while occupied and going down to 65 during the night and when we are away. We could add the outdoor kit to the Navien and try to move to a constant low-supply temp setup. This way, the basement has less of a chance of running in isolation since the 1st floor zone would be running more often. My concern is that this will increase fuel usage? It also negates the use of the Mitsus for heat?
4.) Move to something other than a mod/con boiler:
What are my options here? Clearly this will be costly, but perhaps makes sense if this mod/con is a lemon and/or the wrong type of boiler for my setup.
Other ideas? Thanks!
Mike