Vokèra [A02] fault codewhat it means and how to fix it

A02 is the limit thermostat doing its job. This is a separate safety device from the normal temperature control, wired so that it cuts the burner independently if the primary circuit exceeds a temperature it should never reach. The natural reading is that the appliance is running too hot, but that is rarely what has happened. Far more often the burner is producing heat at exactly the rate it should while circulation has failed, so the heat has nowhere to go and accumulates until the limit trips. Everything on the cause list below is therefore a flow problem rather than a heat problem. The reason to take this seriously rather than simply resetting it is that the heat exchanger is the most expensive component in the appliance, and repeatedly firing it without adequate flow through it is the single most reliable way to destroy one.

1. 1

   Leave the appliance switched off for half an hour. A limit thermostat that is still hot will not reset, and you will otherwise conclude the appliance is beyond help when it is merely warm.

2. 2

   Check the pressure gauge reads 1.0 to 1.5 bar cold. Low pressure and poor circulation very often turn up together.

3. 3

   Open all thermostatic radiator valves fully. Check the service valves on the pipes below the appliance are aligned with the pipe, not across it.

4. 4

   Run the heating for twenty minutes and feel each radiator top and bottom. Cold at the top is air and you can bleed it. Cold at the bottom is sludge and you cannot.

5. 5

   Reset once. If A02 comes back, stop.

   Each reset fires the burner into a heat exchanger that is not being cooled. This is precisely how a £300 pump job turns into a £900 heat exchanger job.