The new meter probably is wired to only switch on the heater when it is on off peak, so it will only heat water for 10 hrs per day. You need an on peak boost heater wired separately to get hot water outside of the E10 hours, do you have a separate heater wired to your tank?
I have got a new E10 meter from EOn installed it last week. But it seems like my electric boiler is not working when i switch it on. Before the new meter installed, i can switch on and off and it was working straight away after i switch on/off but it is not like that after the new meter, E10 installed.