My Navien NR 240 was installed in Dec. 2011 and worked fine until about 3 weeks ago. I started having problems with inconsistent hot water at the kitchen sink when rinsing dishes (on and off flow). It also started taking longer to initially get hot water. Showers worked fine but it was taking a little longer to get hot water. No error codes were observed. I called a service tech and he could not find any problems. Troubleshooting the unit on my own I discovered that the burner was intermittently failing to ignite. A successful ignition took about 10 seconds. If flow is interrupted for several minutes (as in rinsing dishes) the burner will take around 35 seconds to re-ignite and that results in a huge cold water sandwich and takes around a minute and a half to recover to 100 degrees at the faucet. I also found very strong gas fumes outside near the heater vent tube.

Can't live with out it! I have two male small dogs that refuse to give up their marking behavior (both fixed, sigh!) and we always have a bottle of Nature's Miracle.