Ferolli maxima 35s F5 code

[matsm]

Looking for a little help if possible on a ferolli maxima35s

Had an f5 fault code last week fan replaced today and all looked good.
New fan fitted runs for few mins and goes to f5 fault again!

Strange thing is when I put boiler into test mode it will run no problem without a fault to test high and low combustion , the minute I put off test mode it's runs fires up for few mins all looks good then f5 appears .

 

[muggles]

Register for the Combustion Chamber and ask in there - forum rules prohibit answering gas safety related questions in the open forum

 

[matsm]

Cheers , details entered except post code is this my post code or company postcode ?

 

[muggles]

Company postcode probably, that way they can check your Gas Safe registration

 

[Agile]

So the postcode of the gas registration that you work under.