Navien NCB-240E water pressure keep dropping

[bonbon]

Hi, there,
There is a Navien NCB-240E installed in my house one year ago. Recently, in the summer, error code E351 happened once, then I open the auto feed valve to make up some water, the unit works again. But the problem came again in two weeks.

I found the pressure drops 1psi everyday, but not in daytime. It drops overnight. I did not see any leaking in my system. I have two zones in my house. I closed two supply valves and two return valves to make the closed loop by the unit itself. However, the pressure still drops. So, that means the Combi is leaking somewhere.

But, I still could not find any leaking around the unit. I think maybe the water pressure relief is faulty. I am not sure. BTW, the water pressure goes 38PSI and the 30psi PRV is warm and the pipe drips some water to the floor drainage when I turn on the domestic hot water. Is it normal?

Thanks for your help first.

 

[Jadnashua]

Do you have an expansion tank in the system? Any closed system needs one, and you want one specified for use with a hydronic system. It must be sized properly and precharged to your normal system operating pressure. If you have one, it sounds like it has failed.

 

[Sponsor]

 

[bonbon]

Do you have an expansion tank in the system? Any closed system needs one, and you want one specified for use with a hydronic system. It must be sized properly and precharged to your normal system operating pressure. If you have one, it sounds like it has failed.

Yes, I have one. I thought the expansion tank only to do with my home heating system. I have not used heating system at all during last three months since it is in summer. I only used domestic hot water.

 

[bonbon]

Do you have an expansion tank in the system? Any closed system needs one, and you want one specified for use with a hydronic system. It must be sized properly and precharged to your normal system operating pressure. If you have one, it sounds like it has failed.

Thank you very much. I really appreciate your idea. Could you tell me if I change a new expansion tank, how much pressure I shall precharged. Thanks

 

[bonbon]

Yes, I have one. I thought the expansion tank only to do with my home heating system. I have not used heating system at all during last three months since it is in summer. I only used domestic hot water.

The pressure goes to 38psi when I turn on DHW(domestic hot water), while the heating system is off. The pressure goes from 20psi to 26psi when I turn on heating system.

 

[bonbon]

Do you have an expansion tank in the system? Any closed system needs one, and you want one specified for use with a hydronic system. It must be sized properly and precharged to your normal system operating pressure. If you have one, it sounds like it has failed.

Hi, jadnashua,
The pressure goes to 38psi only when I turn on DHW(domestic hot water), while the heating system is off.
The pressure goes from 20psi to 26psi when I turn on heating system.

 

[Alan and Robyn]

Hi bonbon. I know this is an old post. Fingers crossed that you see this. I was wondering how you turn off the radiant heat in the summer? I also have the NCB-240E (installed this past fall) and havent found anything about a summer setting. I tried tech support but they were not very helpful. Thank you for any help

 

[Fitter30]

Expansion tanks have to be piped on the suction side of the main pump. Don't know what type of heating devices your using but 10-12 lbs is normal for most. Air pressure in tank should be same as water pressure on a cool- warm boiler and no water in the air when checking pressure or else the the ex tank bladder is bad. Heating side has a 30 lb relief valve so it's relieving. Lower the pressure.