Weird... unpredictable hot water

[finlaand]

Hi

Had new Worcester Bosch 40 CDi system boiler, new rads, and c80% new pipework throughout house - two zones for heating and one zone for HW.

HEating all good. How water is just unreliable - sometimes it does not heat the tank with enough water - so maybe enough for one shower but no more. I just upgraded the cylinder to faster more insulater gledhill above BS standard - but did not fix the underlying issue.

I am using the thermostat on the tank installed a year ago - could this be at fault?

 

[gas4you]

What position is the tank stat installed at?

It should be about 1/3rd up from the bottom and set for 60C.

Next check the operation of the stat and then the 2 port valve that it controls.

 

[finlaand]

1/3 from bottom as per standard.

Remember this is second tank - had issue also on first tank (which was c20 years old).

As to the operation of the stat, how do you check? I had thought of getting a visual thermostat as a bit of plastic you turn to a setting does not tell me anything , but i could not see one like that to buy and install.

Where would the 2 port value be located, the boiler HW outlet valve i assume (also new last year), and not near the airing cupboard with the cylinder?

thanks in advance