Navien boiler/Taco pump problem

[bonedoc]

Question from a DIY/novice: I have a Navien boiler (model NHB-150) connected to a Taco circulator pump (model 0013-MSF2-IFC), which is one of the recommended pumps in the Navien manual. After about 7 years without problems, the circulator pump started making a loud buzzing noise when in operation, yet otherwise functioned well. My HVAC company came and said it was a loose bearing in the pump, and replaced it. After replacement, the buzzing noise resolved, only to recur months later. They replaced it a second time and the same thing happened. I asked ChatGPT, and it strongly suggested that the problem was hydraulic cavitation (possible causes including suction side air accumulation, inlet restriction, low system pressure etc). After asking my HVAC company about cavitation, they said that they checked for it, and cavitation does not appear to be the cause. They claim to be at a loss for the cause, and the tentative plan is to replace the Taco with a Grundfos model UPS 26-99 (also listed in the Navien manual). Best I can tell as a non-expert, and based on prior experiences with them, the HVAC company seems knowledgeable.

Has anyone encountered similar issues with this specific setup before? Although they claim they checked for cavitation, I am concerned the same thing will happen to a different brand pump. Even if the problem is not cavitation, it seems unlikely to me that the pumps are the primary cause here. Suggestions for how to proceed? Get a second opinion with a different HVAC company?

 

[Fitter30]

Take some pics of the piping, expansion tank, air removel device, boiler and any other pumps. Water pressure with boiler and all pumps off. Type of heat emitters? One or two story house, boiler in basement?

 

[Sponsor]

 

[bonedoc]

Hi, thanks for the reply. It was hard to get a shot of the entire system because the room is narrow, but picture 1 is a panoramic, and picture 2 has the problematic pump circled in red. It's a 2 story house from the 1950's and the equipment is in the basement. Thank you

 

[Fitter30]

Boiler is piped wrong. The two water pipes entering the boiler are not piped to back to back tees they have a filter between them and are futher apart than aloud. 4th pic down pump motor is in the vertical plane needs to be turned to the horizontal. What water temp are you running and type of heat emitters? Page 18 pic shows back to back tees. Taco pump install manual will show pump positions. Also with piping changes boiler treatment would be a good idea something like Rectorseal 8 way boilet treatment 1 qt is good for 25 gallons in system. Nice looking system.

www.navieninc.com/downloads/nhb-manuals-installation-and-operation-manual-en

 

[bonedoc]

Boiler is piped wrong. The two water pipes entering the boiler are not piped to back to back tees they have a filter between them and are futher apart than aloud. 4th pic down pump motor is in the vertical plane needs to be turned to the horizontal. What water temp are you running and type of heat emitters? Page 18 pic shows back to back tees. Taco pump install manual will show pump positions.

www.navieninc.com/downloads/nhb-manuals-installation-and-operation-manual-en

Thank you very much for your feedback!!

A couple of follow-ups:
- sorry I couldn't follow- which is the pump that needs to be reoriented from vertical to horizontal?
- where would I find the heat emitter info for you? (sorry I'm a novice) . I'll check the water temp and post
- most importantly, do you think the errors you have identified are incidental? Or they may be the actual cause of the repeated circulator pump failures I'm describing?

Thanks again

 

[bonedoc]

Boiler is piped wrong. The two water pipes entering the boiler are not piped to back to back tees they have a filter between them and are futher apart than aloud. 4th pic down pump motor is in the vertical plane needs to be turned to the horizontal. What water temp are you running and type of heat emitters? Page 18 pic shows back to back tees. Taco pump install manual will show pump positions. Also with piping changes boiler treatment would be a good idea something like Rectorseal 8 way boilet treatment 1 qt is good for 25 gallons in system. Nice looking system.

www.navieninc.com/downloads/nhb-manuals-installation-and-operation-manual-en

Temp setting on boiler is 167 and heat emitters are old cast iron radiators

Is pump circled in red the one that's misoriented? Looking at the Taco manual, that orientation appears to be "OK' as long as the the psi is greater than 20? The psi runs in the low 20's whenever I've looked

Looking at the Navien manual, I believe the piping is correct (although hard to see in the picture)? Are there not back to back tees, close together, in the red circle? The filter placement also appears correct looking at the diagram in the manual?

Thanks again for your help and your time

 

[Fitter30]

At 20lb system pressure water boiles at 228° f. Cavigation is very hard on impellers. Haven't seen it on a cartridge pump but on large bronze inpellers pumps 25+ hp they look like they were sandblasted to totally 80% gone. Have seen piping like yours with back to back tees work but design is 8 pipe size diameters before and 4 after. Wonder if the filter is dirty or with all the 90°s reduced pipe size that might be part of the problem. With a micobubbler air devise air isn't part of the problem. They are so efficient they pull air from everywhere. Condensing boilers get their efficiency from the condensing flue gas. Return water has to be 140° or below to get to the 95% above 87%. Heat emitters are the radiators. Water is 2.31' per lb of pressure. 10/lbs = 23.1 ' height measured with all pumps off water temp under 100°. From lowest piping to hightest point of the system. Then add 3 lbs. Bladder tanks air pressure adjusted system pressure. But your running at 20 lbs for the one pump.

 

[bonedoc]

Got it. Thanks very much for sharing your knowledge!