American Standard condensing propane furnace lockout issues

ddr

We installed an American Standard warm air furnace in a customers home about five years ago. The system ran fine for years and then...this year has had nothing but lockout issues. The fault code comes up as a 2-flash which is (3 unsuccessful tries for ignition). We verified correct inlet gas pressure-12"WC, correct manifold pressure-6"WC first stage and 10"WC second stage. When fired, the pressure drop is not more than 1.25"WC. Flame signal is 2 micro amps. The primary heat exchanger was cleaned, the fresh air pipe disconnected, the pressure switch closes at he proper settings. The flame sensor was replaced along with the circuit board to try to eliminate grounding issues but still the same thing. The propane tank was filled in the summer and just recently filled again late February. Maybe I'm missing some thing obvious here but what else should I be checking?



Thanks

heatpro02920

ground

normally these issues are ground related, is it a damp basement? Clean all the ground contacts, everywhere, I had one that was driving my techs crazy for almost a week, I went there and is was the burners ground...



Also i had bad boards rite from the supply house, seems some guys like to put their old board back in the box and return them as new...

VictoriaEnergy

2 thins I'd look for....

On a 5 year old old install I'd look for:



1) scaling up on the front side of the in-shot burners, this delays or stops the flame from travelling successfully from burner to burner between the HSI and the flame rod within the control's allowable time limit.



2) On a system with no pilot flame loads; put a manometer on the furnace and look for either very high lock-up pressures, or the opposite, where the the pressure slumps way down to very low pressures before the sticking service reg opens up.  Most often this only does it only after the system has been off for a long time.