LC Lime condition – flush plate heat exchanger

What the control is telling you

Service reminder (when enabled in parameters) that the boiler is due for flushing and service. Lime build-up damages the plate heat exchanger and is not covered by warranty.

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

Likely causes

• Service interval reached
• Lime/scale build-up in the plate heat exchanger
• If it won't clear: DHW thermistor, flow sensor or boiler pump issue

Test and repair steps

1. Shut off the gas supply and turn off the DHW and CH buttons on the controller.
2. Close the hot and cold water shutoff valves (V3 and V4). Isolation valves are strongly recommended to allow flushing.
3. Connect the pump outlet hose (H1) to cold water service valve V2 and the drain hose (H3) to hot water service valve V1.
4. Put four gallons of undiluted, food-grade white vinegar in a pail and place the drain hose (H3) and pump inlet hose (H2) in it.
5. Open service valves V1 and V2 and flush the plate heat exchanger with the circulating pump.
6. Remove the front panel (two screws), locate the PC Board at lower left and press SW3 to clear the LC code.
7. If LC does not clear, check the DHW thermistor, flow sensor and boiler pump.