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Afternoon, I have a Baxi Luna 3 Comfort Combi Unit, The boiler goes on when I open faucets or showers, But goes cold in about 5 minutes tops, Then takes forever to heat up again. Cant even take showers. The unit is 2 years old, I checked the heat exchanger and flushed it out just incase of scaling or slime. Some dirt but nothing to stop water flow. This has been a constant issue. Was a direct replacement with an old baxi unit due to hurricane sandy.
Have you reviewed this Troubleshooting guide from the manufacture? Luna 3 Comfort Troubleshooting Guide. You also may want to look at the water pressure of your water line feed and the baseboard loop. If the loop looses pressure it will shutdown the boiler.
