What does the red light signify? What does the manual say?
See this section:
1:5.2 BOILER OVERHEAT/LIMIT THERMOSTAT
The Boiler is fitted with a safety overheat/limit thermostat. This will interrupt the power supply to the Boiler and
shut it down completely in the unlikely event of overheating.
Should this occur, the red limit indicator on the Control Panel will be illuminated. Wait for the Boiler to cool,
and then reset the thermostat by pressing the limit thermostat reset button located under the Control Panel -
see fig 1.
If this problem still persists, turn off the Boiler and consult your installer.
It appears your boiler is overheating. This may be because of a failing thermostat however it needs checking by a Competent Person.