Rinnai RE140e won’t stay running

Slowhand63

Home built 2.5 yrs ago in warm weather climate. It is our second home. We’ve stayed there approx 10-12 weeks since the home was built. So, although the Rinnai is 2.5 yrs old, it has very few hours on it (this may be good or bad). I know I could have checked the actual runtime but didn’t think to do that when I had the cover off.

I arrived at the house yesterday and have no hot water. We don’t turn the gas off while we’re away. Actually I have a little hot water. I’ve been running the faucets or shower and will get a surge or HW, but it lasts less than a minute and then will run cold. If I turn tbe faucet off, wait a minute or so, it will start cold, then get hot, then cold again. This doesn’t happen every time. At one point with the faucet running the Rinnai ran for a good 10 minutes, but when I put the shower on (I left the faucet running also) it went cold within 30 seconds.

Pulled the cover and checked for error codes. The last 4 were: 12, 12, 11, 11. There were no other codes. Removed the flame sensors and igniter and cleaned them (they had very little carbon build up, likely due to low run hours, so I was not optimistic this would solve the problem). It did not.

What else should I be looking at? I thought tomorrow I’d pull the burner assembly and blow it out with compressed air. Check the fan motor for bugs etc. Look for any other obstructions etc (I didn’t see anything obvious today).

Any other ideas?