Stupid questions about water heating

[thelawnet1]

We have a Potterton Profile 50E boiler. It's set to 'gravity-fed'. Next to it is a Grundfos pump.

Upstairs in the airing cupboard is an electric immersion heater. It looks ancient, I guess from the 1960s. It's a Santon 3kW model.

The problem we sometimes have is hot water running out after several baths. It would seem, given the gas boiler is 12-15 kW output, that the immersion heater is relatively useless except if the boiler is not working.

Given so, is there any way to increase hot water, I checked the thermostat on the boiler is set to 1 (it goes up to 7 or thereabouts); would this determine the water temperature - obviously if the tank stores say 200 litres, then if the water is at 60C rather than 45C or whatever it is now then it will last longer?

Or is there something else I should be looking at to determine the hot water temperature?

[thelawnet1]

So the thermostat knob on the boiler controls, and is the only thing controlling, the water temperature?

Edited by thelawnet1 on Tuesday 24th January 09:53

[thelawnet1]

Yeah it's a rented house, so we can't do much; the immersion heater is often on 24/7 but that seems very wasteful so I wanted to leave it off tbh.

It seems in theory like the only time the immersion heater could be useful is after someone has already had a bath, as the tank should be full and at temperature after 30-40 minutes using the gas boiler alone.

I have an instant heater in my house in Indonesia - it's much easier there, the water comes in at 20 Celsius, and I heat it to around 40. Doesn't take much gas nor a very fancy heater. (Though I still wouldn't use electricity, the average house over there has a 10 amp supply and everything pretty much has to be backed up with a generator).