Ferroli [A03] fault codewhat it means and how to fix it

A03 is high limit protection, a permanent lockout triggered when the appliance reaches a temperature it must never exceed. What is useful about the Ferroli manual here is that it gives two quite different causes rather than the single one most manufacturers list. The first is the expected one: no system circulation, with the manual directing an engineer to check the pump, the radiator valves, and the operation of the internal bypass. The second is more subtle — a flow temperature sensor that is not active or not correctly located.

A sensor that has worked loose from its pocket reads the air around it rather than the water, and can report either a wildly wrong temperature or a lagging one that lets the real temperature run away before anything notices. That is a genuinely different repair from a seized pump, and it is why an engineer should verify the sensor is properly seated before condemning anything expensive. The internal bypass is the third thing worth naming, because it is the item most often overlooked.

1. 1

   Switch off and let the appliance cool for half an hour. A high limit device will not reset while it is still hot.

2. 2

   Check the pressure reads 1.0 to 1.5 bar cold, and top up through the filling loop if it does not.

3. 3

   Open every thermostatic radiator valve fully. This matters more than usual on a Ferroli given that the manual specifically flags the internal bypass — with all valves shut and a bypass that is not working, there is nowhere for water to go.

4. 4

   Run the heating twenty minutes and feel the radiators top and bottom. Cold at the top is air you can bleed. Cold at the bottom is sludge you cannot.

5. 5

   Reset once. If A03 returns, stop.

   Every reset fires the burner into a heat exchanger that is not being cooled properly. That is the most expensive component in the appliance and this is how it fails.