if you have the boiler set to max and runing all day it wont hurt it at all as you boiler if i remember right is a modern combi, it will run at max gas rate till it gets near its high temp then it will cut the gas rate down ( use far less gas) to keep it at the high temp. but if you are still cold then that means that you havent got big enouth rads fitted or you have got a lot off heat loss from your house, hope this helps