Phil L wrote:

A leak is probably the cheapest job to repair...

True, but not if some damage as been done to the property (depending on
where the leak is).

now if it's a faulty boiler....

That said, it's highly unlikely to be a leak - she had hot water this
morning, and if it was a leak, the boiler would be fired up almost
continuously, heating the replacement water lost from the cylinder

Yes, true, but I doubt if she would notice if it's firing continuously
when it's on.
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