When I turn on the hot tap the boiler fires up then a few seconds later it overheats and I get F3 fault code, the pump is running and it has a new flow sensor as this is what the fault finding guide stipulates, I have noticed that the diverter valve was switching to heating when hot water is demanded and hot water when heating is demanded, the diverter valve has also been swapped to see if it was that but still the same fault, the pcb has also been test swapped and so has the hot water flow meter still to no avail! any advise would be greatly apreciated :)

Adrain, January 2009

My boiler pressured right up to plus 4 bars I drained the rad bk down to 1.4 I have no hot water or heating and it's trying to fire up but not ignighting any ideas !? Then the fault comes one to f1

Sam, February 2014

Hi.
Has anyone got the pcb settings for the optimax 31c?

Vtang, October 2013

Hi, you need to reprogram the new PCB with the25C settings. Had the same problem myself, the diverter valve is going to CH when the hot tap is opened causing the chamber to overheat and bang.
The Settings are:
P1-00
P2-06
P3-00
P4-00
P5-07
P6-02
P7-80
P8-04
P9-20
P10-60
P11-00
P12-28
P13-80
P14-85
P15-04
P16-10
P17-20
P18-57
P19-10
P20-15
P21-25
P22-10
P23-80
P24-40
P25-00
(Settings obtained from my old PCB)
Use the power and M button to enter the set up and the radiator dial to adjust.
Hope this helps.

Ryan, December 2010

did Adrain fix his boiler in 2009 if so what did he change mines doing same 03 fault diverter valve going to heating when you call for hot water and pump gos off it bangs a bit then gos off could it be p c b or do i need a new boiler

tony, April 2010

how do you reset the parameters please

dave, August 2009

Hi i would love to no if you have sorted this problem as i have the same boiler and i have the same problems, mine makes a banging and clunking noise f3 comes up when my hot water stops runs for 5 sec then (d) come up,then re set it self and i have no ch, can anyone help me please paul (ps) some one did say it was the diverting valve, reading this one i am not to sure?

paul, March 2009

If you've changed the control PCB you will have to reset the parameters. PCB are set for system boilers so it will o/heat and make all sorts of banging noises b4 F3 comes up.

Gasser, February 2009

The fault lies in the pcb that sits under the gas valve. Is this the pcb that has been test swapped ? Swapping the display pcb won't help you.

Richard, January 2009

have tried fitting a new safety thermostat.
it could be that the pump over run setting needs adjusting.

phil, January 2009