If my megaflow needs re-pressurising, does it mean my hot water will cool faster in the tank until this is done?

[splatfrog]

I put the boiler on for 20mins this morning to make hot water for a bath. This is usually sufficient time. But whilst running the bath I noticed the water wasn't so hot that I couldn't keep my hand under the tap the whole time. (not using cold at all). Is this an indication that the megaflow is way overdue re-pressurising?

If I ever completely empty my megaflow tank of the hot water, I noticed it needs an initial longer burst of 1.5 hrs to get it back to hot going forwards (in case that helps)
e.g after coming home from hols.

As far as I'm aware, the megaflow is not heating anything, merely storing the hot water the boiler produces? It's not being used as an immersion heater.