Navien NCB240E Pressure problems

[Karl Lucas]

My Navien Combi Boiler installed Dec 2019 consistently runs at a high pressure - 27-30psi.

The following conditions exist:

• I have a 4-zone system with Tac0-570-2 valves in a 3,000 sq. ft. home with highly oxygenated well water;
• when first installed it was not set for fin radiators- that was corrected in the first month, the techs bled at the radiators throughout the house;
• it was not set for well water as the source- that was corrected Oct 2020;
• the over pressure releases frequently at times- occasionally every 90 seconds, especially in the morning, then less frequently during the day/night. The morning releases will occur with no zones operating and no zones calling- and no DMW call either- there is a thump, thump, thump, thump and then a small amount of water is released;
• there are no error codes displayed- except once-when our power was out and came back on, then it said "air".

I have inquired about a pressure reducer. The tech said it has one built in and Navien does not recommend adding one. I inquired about an air separator and was told it was built in as well as on the tank.

I don't know if I should try bleeding the system at the TACO valves? I don't know if it would help with the water being added having a high oxygen content. They installed several 3-way valves so the system can be bled using a hose connection to the DWS instead of relying on the system adding water.

Any advice would be helpful. The techs from the installer/service are trying their best- but I don't believe they have a lot of experience with these units.

P.S. Tech just arrived to review the unit and settings before consulting with Navien- I'll post anything that results.......

 

[Fitter30]

What is the complete model number. Is the house one or two stories? Are you heating with fin tube or ? Take some pics of the combi and piping.

 

[Sponsor]

 

[Karl Lucas]

Thanks for the rapid response. The tech purged the zones as well as the unit. In talking with Navien they felt air was probably coming in through the Taco valve that has a very slow drip...... so $400 estimate to replace the taco valve and add a three way ball valve and purge the system again. Hopefully this will cure it. I was planning on replacing the Taco valve(s) myself this coming spring (and another that isn't currently leaking) because their original estimate was $1,100 to replace two Taco valves and upgrade to the ball valve..... I'm happy to do the work myself but I guess the $400 isn't too bad..... I'll do the other valve, etc. myself this spring. I probable should have had the valve replaced as part of the install- the corrosion/oxidation in the photo was there at the time- but wasn't dripping.

 

[Fitter30]

Taco heating valve leaking without taking a wire brush to clean both valves to see exactly where it leaking. Both can be taken apart and resoldered. If the taco valve itself was leaking it would be leaking from the top of the body not at a pipe connection. The red bell and gosset expansion tank, need to know where in the system is piped in relationship to the main pump. The tank should be on the suction side of the pump not the discharge (arrow on the pump for flow)