Navien NPE-240s - Constant Temp Fluctuations

[aeneas01]

recently moved into a new home (that was used only as a vacation home, occupied mostly on weekends, about two weekends a month) - it came equipped with a navien npe-240s (no internal recirc pump and no after market exterior recirc pump added) that was installed 6 years ago, the interior of the heater is immaculate, looks brand new, unfortunately faucet and shower temps constantly fluctuate up and down every 30 secs or so, from very hot hot to luke warm, hoping to get to the bottom of this!

what i've done in an attempt to fix the issue:

- thoroughly flushed/descaled tank, cycled vinegar for an hour
- all filters were almost completely clean before i flushed/descaled, water inlet filter had a few lime crumbs
- removed flame rod assembly and sanded rods (altho they were already in very good condition), replaced gasket
- replaced flow sensor and o-rings, propeller on top section of replaced sensor seemed worn
- turned dip-switch to on for lp, all other switches in off position (previous owners converted unit to lp but switch was never turned to on)

none of this solved the problem, the unit behaves exactly as it did before i did the above.

other info:

- water in our area is soft
- tested with multiple faucets turned on, water temp still fluctuates
- water temp is set to 120 on the navien, however the navien info panel shows the out water reaching temps of 140+ when hot water is turned to max, is this normal?

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here's a short vid of the navien with the closest water faucet turned on at max hot and max pressure/volume, the water out reads 0.8 gpm.

at 94f the burners turn on and the temp starts to quickly rise until temp reaches 149f, this takes about 23 secs, burners then turn off turn off and fan turns on, temp starts to drop quickly until it reaches 94f, fan seems to turn off at at around 110f, this takes about another 23 secs, then the cycle starts again and repeats until hot water is turned off.

what else can i try? would a factory reset help? and assistance would be greatly appreciated!

 

[Fitter30]

Measure flow and unit reading. Bath tub or pull the shower head. Use a bucket and time then measure. 1 hour for a unit that might have been cleaned in 6 years might not be long enough. Cleaning vinegar is a little stronger. Look at page 91 Capacity setting
Service manual
www.manualslib.com/manual/1358915/Navien-Npe-180a.html?page=1#manual

 

[Sponsor]

 

[John Gayewski]

Check valve, it's easy to change. Order one. It's always the check valve.

 

[Old saggy house]

The 240s doesn't have a check valve.

There is a mixing valve on the heater in the cabinet just above the hot water outlet

I had similar issues. My mixing valve was also leaking.

I took the mixing valve apart. There are a few o-rings that needed to be cleaned and regreased. There are two parts to the mixing valve. You will see it when you pull it apart.

There is the electronic stepper motor and then there is the valve. When you separate the two you will see that there is a diagram on each. It shows you how open or closed they are from 0 to 340°

You have to zero out the valve and zero out the stepper motor when you put it back together.

On my first try I didn't get them back together right. I was off one tooth. It was clicking so I took it back apart and put it back together. That was 3 months ago.



On both the valve and the stepper motor there is a 0-340°

There's more than one mixing valve on this unit but the one that was causing me problems was the one right above the hot water outlet.

 

[Fitter30]

The 240s doesn't have a check valve.

There is a mixing valve on the heater in the cabinet just above the hot water outlet

I had similar issues. My mixing valve was also leaking.

I took the mixing valve apart. There are a few o-rings that needed to be cleaned and regreased. There are two parts to the mixing valve. You will see it when you pull it apart.

There is the electronic stepper motor and then there is the valve. When you separate the two you will see that there is a diagram on each. It shows you how open or closed they are from 0 to 340°

You have to zero out the valve and zero out the stepper motor when you put it back together.

On my first try I didn't get them back together right. I was off one tooth. It was clicking so I took it back apart and put it back together. That was 3 months ago.



On both the valve and the stepper motor there is a 0-340°

There's more than one mixing valve on this unit but the one that was causing me problems was the one right above the hot water outlet.

Never seen a stepper motor for a mixing valve. Usually it a bellow that temp moves it and controls volume. Problem that I've seen with mix valve the cartridge contain passages that get mineral / limed up. Buy a new cartridge to get water flowing and dump the old cartridge in vinegar for a few days to clean it up for a spare. The hight the water temp the heater is putting out the more minerals are being drove out of the water and heater will need to be cleaned more.