720 Flame rod fault

What the control is telling you

Fault in the flame sensing (flame rod) circuit.

Applies to: I-Series Plus boilers — 150K BTU and smaller and 175K BTU and higher (Combi and Solo)

Likely causes

• Frayed or broken flame rod wiring
• Loose flame rod in porcelain housing
• Cracked porcelain housing
• Flame rod touching metal or wet
• Heat exchanger leaking onto flame rod
• Weak flame signal (below 1 µA)
• Failed PC Board

Test and repair steps

1. Inspect the flame rod harness for frayed or broken wires and damaged connections.
2. Check that the flame rod is tight in its porcelain housing and the porcelain is not cracked.
3. Make sure the flame rod is not touching metal and is not wet.
4. Measure flame rod current; it should hold at least 1 microamp.
5. Replace the flame rod and its gasket.
6. Check whether the heat exchanger is leaking and dripping on the flame rod; if so, replace the heat exchanger and flame rod assembly.
7. If the flame rod and wiring are fine, replace the PC Board.
8. Before swapping the PC Board, write down all parameter settings, then copy them from the old board using the data transfer cable supplied with the new board (see the part's instructions).
9. If data transfer fails, re-program all parameters and set gas valve values per the Installation and Operation Manual (150K and smaller: also see docs 800000253 and 800000254).