Hot water tank replacement

Money_Saver

After some advice:
Had  a new hot water tank installed and I have a problem with the hot water. I set the timer for  2 hours to get "hot water" anything less, is just lukewarm. (previous tank was on for about 1hr 30m and the water temperature was fine. Firstly, the engineer advised to increase the tank thermostat from 60c to 70c. This has indeed increased the water temperature. However, the hot water isn't lasting for long once it's stored. Its a 117 litre tank. I have checked the 3 port valve and it's switching over from heating/hot water, so I am at a loss as to why the water isn't holding its temperature.
The water comes on at 03.30 for 2 hours and then by 11.00 it's lukewarm and runs cold, despite only having a approx 7 minute shower. I have noticed when I use hot water, the tank is replacing the water I have used with cold as I hear the mains filling?
The tank is insulated.
Can anyone shed any light as to what could be wrong?

Thanks

Richie-from-the-Boro

Are you on an E7 tariff? In which case you should get 7 hours of very hot (legionella) water in your Part L compliant. High efficiency foam insulation and 22mm compression connections and fittings.

E7 will have two (bottom + top) heating elements. The top is small amount 1 or 2 houru top up, the bottom is 7 hour full tank.

See here: https://www.screwfix.com/p/rm-cylinders-indirect-vented-ss-cylinder-162ltr-1060-x-450mm/93313

Money_Saver

No, not on E7. The tank is Gledhill Envirofoam 
Here is the tank 
https://www.manomano.co.uk/catalogue/p/gledhill-117-litre-envirofoam-copper-direct-vented-cylinder-8311362

Richie-from-the-Boro

Ok, it's 'ErPC' not B, and minimum standard, running I assume through an off.peak controller.into two standard 3kW heating elements. 2 hours @ 2kW should be enough to sufficiently.charge this with hot water. Clearly it does not. I wonder if it's only on a single element/very cold draught area/just poorly set up or undersized for its needs.

Mister_G

Since the OP is talking about a 3 port valve, I assume that they are heating it with either oil or gas.  Therefore the electric side of things is irrelevant?

Money_Saver

It was a faulty thermostat on the cylinder

Mister_G

Thanks for the update.  Hopefully that will help someone else with a similar problem.