Over pressure can either be caused by putting in too much water through the filling loop or the cold start pressure being too high say over 2 bar when it should be 1- 1.5 when cold. Or the expansion vessel is depressurised Ie knackered as shown by the water pressure rapidly moving from 1.5 to 2.5 on the pressure gauge after running the heating . You will also find that the pressure relief valve starts to leak outside after 2.5 bar meaning you have to constantly top up the boiler ....a bad situation that rusts all your radiators from the inside out . A new vessel is around 150 all in with fitting or 1.5 million pounds for a bodger to do it in London.
Howieshelps
November 2015
I followed the advice above, it worked fine. The F21 fault is not listed in the manual but is 'too much pressure'. Bleed when cold ideally, but I suggest you take the pressure down to 1.0 when cold. The dial is underneath the boiler on the right hand side by the way!
Janet
April 2013
f21 code is to much pressure in heating system bleed system on cold back to 1.5 bar pressure from a rad
mk gas
December 2010
could you please tell me how to set the time for the heating to come on and go off at different times of day
peter
December 2009
jus
t fitted the above ferroli 31 .worked for one day your service engineer did not turn up today . client wan ts me to rip it out what do i do know and who pays me dpcullis
dpcullis at k and j plumbing services
November 2009
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