Hi can any one help , i have a grant vortex 26 combi boiler and it does not seem to be heating the stored water . The hot pressure is bad and have read that the stored water has a pump to help pump it to taps and the boiler used to fire up all the time which would heat the stored water but it is not firing up except when taps are turned on .We have hot water but pressure is bad . Any ideas please let me know .thanks