Monitor 422 Fuel Issue

[alaskajerry]

I have a Monitor 422. It will come, on fire up and the fan will come on like normal. After it clicks into high burner status it will run for about 2 minutes and then it begins "thumping" like it is out of fuel. I have cleaned all the filters and I replaced the fuel pump but it still does the same everytime. I restart it and it will pump the fuel in and burn but again it will burn on high for about 2 minutes and start "thumping" again and will shut down. It seems to get the fuel just fine in the beginning. Any ideas on what the next step should be? Thank You!

[HayZee518]

fuel problem

how high is the external fuel tank outlet "above" where the tubing enters the house? if the tank outlet is below the tubing line, the level in the tank should be a minimum of 18 inches. your heater is starving for fuel.

[alaskajerry]

I am only using the internal tank.