I heard "geezer" (?) on "Rumpole of the Bailey" as a character said that her husband, who she was feuding with, had "locked the geezer" (unsure of spelling)...or locked "her geezer"...It was NOT used as a reference to an old man !
In UK slang geezer (or geeza) can just mean a man, regardless of age, like 'chap' or 'bloke'.
In the context of Rumpole of the Bailey, I'm guessing she's saying that he "locked her man up" (put her husband/partner/boyfriend in jail).
Before central heating became common, people often used to have small wall-mounted gas water heaters in their bathroom or kitchen, known as 'geysers' after the famous hot springs. If you are certain it doesn't refer to a man, this is the most likely interpretation.