My tank thermostat only works once a day!

[oldandworried]

I have an ESI ESCTDEB Electronic dual cylinder thermostat fitted to a Stelflow 205l unvented tank wired to a timer going off at 10pm and on at 6am. Every morning the water is hot but gets cooler during the day. The thermostat only calls for hot water first thing. I can push the reset button which makes it call for hot water and the same effect is achieved switching off and on the power for a few seconds. Again only one heat cycle as far as I can tell.​

Am I right in my assumption that the stat (5 years old) is faulty? Are there any other possibilities?
A direct replacement seems the easiest option but these appear to be internet only. These ESI stats seem unnecessarily complicated and suspiciously cheap.
Is there an alternative that you professionals would recommend please? Is this one from Plumbfix Strom SSCTDS01 Aquastat Dual-Cylinder Thermostat better? I'll get a professional to fit it.
Thanks for any advice.

 

[townfanjon]

Yep it sounds like its **** , they are very popular and cheap , you could change it for an old school imit stat .

 

[Murdoch]

Forgive me for asking this but why can’t you change the time setting on Your central heating controller?

 

[oldandworried]

Thanks the stat sits in a purpose made pocket. I can change the time settings. The hot water is on a pumped loop and it and the stat are on a separate timer.