shab

Hi I have vaillnat 938 ectotec boiler installed.3 months ago the problem with it is when hot water tap is opened even for 4 seconds and closed the heating doesnt resume after 2 minutes. Vaillant have told me hat this is normal and it takes this time to replenish the actostore even though i have comfort mode turned off for the hot water. please help me find out if there is a flaw with the boiler or a fault. thanks