valient eco pro pressure gauge?

The pressure is in the red when the heating is on, when it is turned off it loweres, can i lower this myself, the heating has not been working correctly since before xmas showing error code f28, a plumber called and said we needed a spark plug and a gas valve, and these parts could only be fitted after the new year, I have tried the boiler again today and it has come on and stayed on but the valve gauge is in the red, that is on the front of the boiler, am i ok to leave on as we have had no heating at all and it is lovely, or is it dangerous. thankyou