Heater fires runs for 2min.service heater lite comes on has code 8 shuts down

It is most likely the thermal regulator located in between the inet and out pipes on the manifold behind a black plug remove the plug be carful thereally is a large spring being the plug attached to the thermal regulator. Remove the regulator and look for any corrosion if any at all replace the regulator if not drop the regulator in hot water and see if it completely opens if not it is the regulator

This issue sounds tricky. I recommend you callthe Sta Rite technical support at 888-782-7483 and they should be able to helpyou figure this issue out.

I hope this helps.