Navien Tankless problem

Scotsman62 · Saturday at 10:28 AM

We have a 7 year old Navien NPE-240A (NG) that has had regular maintenance such as cleaning of filters and descaling annually. We did have issue back in early summer when it went down, (no power) fuse was blown and having the fuse replaced didn't correct the issue. Plumbing and heating contractor contacted Navien tech support, advised to replace the circulation pump and control board, when that didn't fix the issue then Navien tech support advised to replace ignitor and flame rod, finally that solved the issue. New issue is an occasional "backfire" (it took me a while to figure out where the noise originated) Unit still working and no codes. OK, so the closest Navien Service Specialist is 100 miles away, Navien will only talk with contractor, any Navien experts with any thoughts as to what our problem is would be appreciated. Cheers!

GReynolds929 · Saturday at 2:11 PM

When does the noise happen? On startup? While running? On shutdown?
If fuel is predetonating there is usually a fuel mixture issue. Have gas pressures been checked when the parts were replaced. Why was the pump and control board replaced, was a short diagnosed? When the PCB board was replaced did the dip switches get set properly for the unit and gas type? Could we get a piictures of the overall install, piping under the unit, cover off, front panel and PCB dip switches.

Scotsman62 · Saturday at 5:36 PM

Scotsman62 · Saturday at 5:54 PM

GReynolds929 said:
When does the noise happen? On startup? While running? On shutdown?
If fuel is predetonating there is usually a fuel mixture issue. Have gas pressures been checked when the parts were replaced. Why was the pump and control board replaced, was a short diagnosed? When the PCB board was replaced did the dip switches get set properly for the unit and gas type? Could we get a piictures of the overall install, piping under the unit, cover off, front panel and PCB dip switches.

Noise does not happen at start up, I'm guessing it happens either when running or at shut down ( I've never been in the mechanical room when the noise happens, I have heard the noise when upstairs or outside) the local plumbing and heating repair man had the discussions with Navien with respect to troubleshooting and repairs at the start of summer. I'm guessing the DIP switches are on the PCB board? I don't feel comfortable pulling it to photograph them. I do not think the repair man checked anything with regards to gas pressure or ventilation when the 4 parts were replaced

GReynolds929 · Saturday at 11:02 PM

From looking at the pictures nothing stands out to me as abnormal. Normally a boom/backfire type noise is during startup not while running. Are you able to replicate the problem while being at the unit, (IE have someone running water and see if it will make the noise?)