Is it possible to adjust hysteresis (or PID) of the blower motor on Navien NPE-240?

[BenT123]

I have an automatic water faucet which makes the hot water output jump between 0 and 1.6gpm which in turn causes the exhaust blower oscillate between 2000 and 4000rpm. Is there a 'secret' setting to delay blower slowdown by a few seconds?

 

[GReynolds929]

No, it controls the fuel air mixture for proper combustion. It's determined by water flow demand. Messing with it the combustion is a good way to get hurt or worse. A better idea would be to address the faucet.

 

[Sponsor]

 

[Fitter30]

Only factory service might be able to change the whole burner operation. Ran some numbers 60° cold, 120° hot 105° mixed, 1.6 gpm total, .4 gpm 25% cold , 1.2gpm hot ,75% hot. By throttling hot water down to 1.2 gpm might help or playing with the wh setpoint maybe raise or lower it by 2° at a time. Just change the to f and gpm/ minute by touching the boxes. Flow sensor reading close? .

Water Mixing Calculator | Spirax Sarco

This calculator will help to consider the mixed temperature of two water streams, its flowrate, percentage flow and actual flow of each stream.

www.spiraxsarco.com

 

[BenT123]

Ok, so air fuel mixture is fixed to BTU output and BTU output depends on water flow. I guess I would prefer that the water heater would dump higher temperature water to the buffer tank and temper it down with a mixing valve. That way the burner output can be more steady: heat water to 140 degF, pause (or lower the heat output), wait until water temperature in the buffer tank drops to 120, turn on the burner.

It takes ~20 sec to raise 0.5 gal of water by 20degF at 15000BTU (minimum) output, so theoretically it should be possible.

@Fitter30 Could you explain why turning the water flow down to .8gal ( hot water) would make a difference? Is it because of turndown ratio?

 

[Fitter30]

Don't know where you got .8 gpm. Have you tried no recirculation? Switches 1-2-3 off. Do have recirculation of any kind? Wonder if the check valve discharge of internal pump is hanging open navian has had some problems with it.