Pentair Mastertemp 125 backfiring

[DallasPentairProblem]

My pentair is backfiring. It was running fine and then one day i notoced it had shut off. When i turned it back on it would run tor about 30 seconds and backfire, usually shutting right off. Sometimes it will continue rhnning and the back fire a few more times until it shuts off.
I have clean out the flu beat i vould without taking apart. Blew air in and shop vacced out.
Any suggestions??

 

[1poolman1]

My pentair is backfiring. It was running fine and then one day i notoced it had shut off. When i turned it back on it would run tor about 30 seconds and backfire, usually shutting right off. Sometimes it will continue rhnning and the back fire a few more times until it shuts off.
I have clean out the flu beat i vould without taking apart. Blew air in and shop vacced out.
Any suggestions??

How old is the heater? Has it been used in very-low temperatures to heat from cold?
The only time I have seen that condition is with a "burned-out" flame holder (the actual "burner") that has been damaged, usually by condensation. Condensation is an issue with pool a heater that is used to heat a body of water that is very cold on a regular basis. But that may not be the only way it was damaged, but is the major one.
Usually, if you remove the blower you can see the condition of the flame-holder.

 

[JamesW]

I have cleaned out the flue best as I could without taking it apart.

What made you think that the flue needed to be cleaned?

Was the flue dirty with soot?

Possibly a sooted heat exchanger.

Is the heater indoors or outdoors?

Is it natural gas or propane?

Can you describe the gas line (Size, length and pressure)?

Did you check the gas pressure static and dynamic?

What date was the heater installed?

Pictures of everything?