No Hot Water!

[Muushy]

Hi everyone i am new to the forum. i got a call today and the person has asked me to go and look at there plumbing system as they have no hot water. they said that the last day it was scalding hot and now there is no hot water whatsoever. Would this be because of a faulty cylinder stat? if so are they easy to change and are they expensive?

 

[ajs heating]

need more info on the system.
is it heated by boiler or immersion ?
is the boiler kicking in when called for hw ?
is the programmer calling for heat ?
is the programmer giving power when hw called for to cyl stat ?
is the cyl stat switching to give power to pump and boiler ?
is it a s plan or y plan system ?
or gravity hw c plan ?