Navien NG NPE-240A Temp fluctuations tried everything

[nicksports321]

I have a Navien NG NPE-240A about 4 years old. My issue is water going cold during a shower and not staying hot continuously. If turn the sink faucet on while taking a shower the chances of it staying hot is higher.

I descaled the unit yesterday along with cleaning the air intake filter. Replaced flow sensor and check valve and also replaced the shower faucet cartridge. Then using the sand paper provided by navien I clean up the flame rod.

Any help will be greatly appreciated. thank you in advance !

 

[Fitter30]

Turn a bath tub on full hot. Check exhaust/flue gas temp, water temps in and out, gpm. Shouldn't very much at all. There is also there is a water adjustment valve that might be stuck code E434

https://www.google.com/url?q=https://irp.cdn-website.com/5486d14b/files/uploaded/Navien%2520NPE%2520Service%2520Manual.2015.09.01%2520%25281%2529.pdf&sa=U&ved=2ahUKEwjomb3ptMqRAxUZtokEHTB4BG4QFnoECAIQAg&usg=AOvVaw14s-m0fPeH6EuiDwlIXx_0

 

[Sponsor]

 

[Breplum]

Check that you don't have any potential cross connection. Some pressure balancing shower valves go bad and cause cross connections. Turn off cold water at WH, open hot valve somewhere or at the pressure relief. Pressure should decrease down to zero on the hot side.

 

[John Gayewski]

Water adjustment valve.