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Ariston Microgenus 24HE MFFI – error code E33 / E34

posted on 24 Dec 2014

Ariston Microgenus 24HE MFFI combination boiler breakdown. Symptoms were as follows:

– boilers starts and temperature goes to about 40 degrees on DHW. After about 10-15 seconds burner goes out while pump and fan keep running.  Boiler displays error code E33 or E34. Water gets luke warm from the tap. Boiler does not go to lockout. After short while burner goes on and boiler cycles.

Codes E33 and E34 indicate APS fault. (Air Pressure Switch). It does not always mean that the switch is faulty. In most cases it means that the fan does not put enough pressure on the switch. Reasons for that could be following:

  • restriction in the flue ways
  • fan failing with age not putting enough pressure on the switch
  • blocked silicone tubes from the fan to APS
  • blocked venturi

In case of this particular boiler it turned out to be failing fan which got replaced with a new one. Faulty fan removed from this boiler below.

In my experience this fault can be repaired in majority of cases without need for replacement parts. Repair should not take longer than 30 – 45 minutes depending on access to the boiler and should cost standard call out charge.

If your Ariston boiler needs repair please contact me here.

Picture of another Ariston Microgenus 28HE MFFI  displaying error code E34. This particular boiler was fixed without need for any spare parts.

This is after the repair – no more error codes and boiler working properly displaying current temperature instead of an error code.


Update 3 Dec 2016

Another Ariston Microgenus suffering from E33 / E34 error codes below:

Boiler after repair that in this case required a major component replacement.