have had problem with boiler not firing,display shows F5,points to the pressure switch,the fan was running and pressure switch operates if you blow down the tube ??? In the main fan and burner housing there is a small flap that sticks. You have to remove the whole unit,seperate the fan from the housing (2 x allen bolts) free the flap then cut away the rubber seal that the flap sits on with stanley blade(this is what viessmann told me to do).You do have to turn off the gas and disconnect it so get some one gas safe to do this,the whole job takes 15 mins . The flap is not on any viessmann diagram by the way.Couple of spade connectors to pull off too. Boiler up and running !!
viessmann 100 f5 fault
- Thread starter oscarbeenladen
- Start date
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hairdryer often works on the F5 flap problem, mixture baffle is the name if memory is correct
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