Proflame (SIT DFC): pilot lights but main burner will not light or drops out

What is going on

Proflame system: pilot proves but the main burner will not come on, will not stay on, or does not modulate.

Likely causes

• Pilot not engulfing the sense electrode, poor sense connection or ground
• Thermostat mode with no call for heat
• Pilot hood not aimed at the main burner
• Main burner orifice wrong or partly blocked
• Valve outlet pressure out of spec
• Failed gas valve, DFC, stepper motor, transmitter or receiver

Check in this order

1. Pilot will not hold make sure the pilot flame fully covers the sense electrode tip, clean the sense cable connections, check the pilot ground cable, then replace the sense electrode/cable or pilot assembly; check pilot orifice and pilot flow adjustment.
2. Main burner will not light check the remote is not in thermostat mode without a call for heat; check wiring; check the pilot hood directs flame to the main burner; check the main orifice.
3. Check outlet pressure at the outlet test point against the appliance spec; out of spec = replace the valve.
4. EV2 test meter between EV2 (green base) and the valve body, system OFF, then turn ON. After the pilot proves, EV2 should spike to about 5 VDC for about 2 s, then hold about 0.6 VDC. Sequence correct = replace the valve; sequence wrong = replace the DFC.
5. Main burner lights when only the pilot should: replace the DFC, then the valve.
6. Does not modulate check main orifice, outlet pressure limits; manual HI/LO version - turn the knob and watch the flame (no change = replace valve); stepper version - inspect stepper wiring (damaged = replace valve), then try a new transmitter, receiver, then valve.

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