A Man With Many Knobs

Today we had our Boiler checked over.  One thing I knew about was the water temperature control knob was broken and, as the boiler has a certain amount of age to it (around 40 years), a new replacement was not available.
"Hold on" said Jan (the heating engineer) "I'll look in my van". He returned with this large bagful of every knob ever fitted to any gas appliance in the last 100 years.  And he had one that fitted.....What a star :-)