Peerless boiler shortcycles

[fearingpeerless]

Hi, and thanks in advance for your help. I have a Peerless Boiler model series MI/MIH. I recently noticed that it has been cycling all wrong. It fires, and the main burner lights and goes out immediately. It may do this once or twice, then the burner will fire, stay lit for 45-90 seconds, then go out again. I keep my home at a cool 64 degrees, but with Michigan winter temps in the single digits at night, even this is difficult to maintain.
I have cleaned the flame sensor rod to no effect. I've checked and adjusted the pressure in the surge tank. The pump is running, the water is heating, but I'm pretty sure this isn't the way this hot water boiler is supposed to function.

 

[Dana]

A pump can be running and not moving much water if the impeller is damaged, which could result in 50-90 second burns if it's moving almost no water. But that would not cause the burner to take multiple ignition cycles before establishing a steady flame.

I suspect either the gas pressure or gas regulator is off, or the gas valve in the boiler is defective. Diagnosing this needs a site visit from a competent tech.