Press i and plus on the front panel you should then see d.0 press the i button and it will display the current rating will range from 5 - 30
Be careful with what you choose as you could be in for a whole world of pain. Can you do a test for me, call for CH when up to a flow of say 65c turn the boiler down to say 50 the boiler will then switch off. Now crank up the boiler stat again to 70c and see if the boiler only fires for around 15 seconds only? You can also do a similar thing with the DHW stat ie when satisfied turn the tank stat up a bit and wait for the flow and return to get near to target temp. Then turn stat down so the boiler goes off, then up it again and see if you get another short cycle. If your boiler cannot get past the 50 seconds intial burn after the first extended burn you may well find going for advised controls may give you a headache.
You could prove its undersized by seeing what d0 in the boiler settings is currently at. Then reducing it to d0 = 16 kW which is far more likely.
Tony
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