Burner shuts off - gas supply issue?

ConfusedandCold

My Rinnai hot water heaters has worked fine for 4 years, but recently it comes on perfectly but shuts down to a code 12 any time it needs to shift to high fire. The gas pressure read a 9 but drops to 1.5 or less when the unit is heating water.

It looks as if it is not getting enough gas and the flames just dims and shuts off.

If I turn off the water flow, it automatically resets and can start again by its self, of course it will only stay on if one faucet is on. The minute we turn on a shower or another faucet it shuts down again.

I have had two plumbers look at it and no answers. Regulator has been replaced and gas company checked pressure to the house.

What would cause the gas supply to drop like that when the unit is running? One plumber is suggesting we need to replace gas lines other does not have a solution yet.

Help!!

JUGHNE

Which side of the gas valve was the pressure reading taken on? The inlet or outlet. It is good to watch both sides during operation. If the gas pipe size worked for 4 years it still should be good.