240A Check Valve or Flow Sensor?

[Steven Karesh]

Hello all,
I've had a Navien NPE 240A for almost 2 years now with no trouble at all... started getting intermittent warm showers and water at the sink instead of hot... now it's pretty much constant.

Checking the display on the unit, it shows that it's putting .75 to 1.25 GPM @ around 110 degrees. Normal operation is hotter with more GPM...

Most of the internet searches bring me back to this forum, so I thought I'd ask here.... from what I have been reading this could be the Flow Sensor or the recirc check valve. Am I right? How can I tell which? (recirc has been internal since installation and this is the first problem I've had)

Thanks in Advance!!

 

[Bannerman]

I suspect the check-valve.

If the check valve is permitting reverse flow, cold incoming water can mix with hot water exiting the unit. The additional water flowing to the WH outlet will not be measured and because cold water is mixing with the hot after the heat exchanger & buffer tank, the temperature flowing to fixtures will be lower than the set temp.

The diagram below shows the correct flow direction from left to right through the pump. If the check valve is not fully closing, cold water entering the Domestic Water Supply connection on the right, will flow left through the pump & 2-way valve to the Hot Water Supply connection and out to fixtures.

The pump will not run continuously so the pump cannot be relied upon to ensure flow is always in the correct direction.

 

[Sponsor]

 

[Fitter30]

Have you ever cleaned the heater with a pump and vinegar? All water and air filters ? What is the water temp setting?

 

[Steven Karesh]

Thanks!
Temp setting is 130.
I've done the air intake filter, but that's it. I just ordered a pump to do the vinegar thing.

 

[Steven Karesh]

Google is showing me a variety of 'check valves' and also mixing valves... which part number should I be going after?

 

[FDNY/RETIRED]

I agree with Banneran if it is a part. BUT since you have no error codes I would do what Fitter30 says first. Clean the unit out with vinegar. My old DPW120A was notorious for needing the DHW side cleaned every 6-8 months.

 

[Steven Karesh]

Fixed it!
The gunk that came out of the trap on the bottom was all gooey and sticky, the recirculating valve was stuck open with gunk and the vinegar that came out was all nasty and brown.
Replacing the valve was dead simple, and flushing with vinegar was pretty easy too; now that I've done it once I'm sure I'll spill less next time!

It's nice to have hot water again, big thanks to everyone for the help!