Apologies for my, frankly daft, posts earlier. 😵
There are two issues here.
1 - heating times.
2 - possible problems.
1. The time it takes to heat your water depends on a number of things. At 8 years old it is possible the internal heating coil is quite scaled. That will inhibit transfer of heat into the water and slow it down. I do not know how our system is configured, but if you are trying to heat your home AND your water at the same time that will be a slow process. Better, far better, to heat your water when your heating isn't being called for. Our for example, runs from 04:00-06:00 and then we 'top up' 12:00-13:00.
Only by testing how long it takes for your cylinder to be 'satisfied' will you be able to work out when and how long to have your hot water on for.
You need to check your cylinder stat. It should be set for 55degs C where it is. That will give you 65 deg water at the top of the cylinder. Water in a cylinder is stratified. It has different temps at different levels. Hottest at the top coldest at the bottom. As a consequence as you use the water, the cool mixes with the warm and you get delivered luke warm water quite quickly. If you want a full tank of water at the same temp, then you have installed an anti stratification pump. This circulates the water INSIDE the cylinder so it's ALL the same temp.
So, some work and investigation to do.
Moving on to possible problems. Your cylinder needs annual maintenance. This maintenance must be carried out by a G3 registered plumber. At the very least, they will ensure your cylinder is operating as best it can under its installation circumstances. It may well be that one or more of the safety valves are letting by and slowly releasing hot water to drain. To me, of much more importance is that the sacrificial anode is regularly maintained to minimise internal corrosion in your cylinder so that is lasts as long as it can. Regardless, to NOT maintain it means you risk it becoming a very serious safety issue in your home. I kid you not.
Get an experienced G3 engineer round and they will advise as to your options.🙂
