Hello Everyone. It's my first post here. Thank you in advance for any help you can give me with my issue. I have a Takagi Tankless water heater from 2012. I understand how scale builds up inside the pipes and how to flush the tank to remove the scale. But looking down into the water heater with the vent pipe removed, there is a Pitina colored build up on the exterior of copper coils/fins. Not alot but it's there. The blower fan blows air through these coils and then vents to the outside Is that build up on the copper coils from condensation? ...If so how do you go about cleaning that? i never see maintenance procedures dealing with this build up on the exterior of the pipes. The underlying issue is that when the water heater is under high demand, the flame which is a perfect blue will shoot up an orange flame on and off and then the flame will go out completely for just 2-15 seconds and kick back on. It will only happen once. And that will happen maybe only a couple of times per week. Of course when this happens anyone taking a hot shower gets hit with cold water for about a half a minute. It's my thinking that this flame issue would more likely be caused by an air flow issue rather that scale build up inside the pipes. Which is why I think the exterior build up may be the cause. For the record, when there is a call for hot water, this unit kicks on the blower fan and draws fresh air from inside the room. This is an indoor unit. Thanks!!!