can anyone offer practical advice?

Thorn Back boilers can be very awkward to relight as the pilots tend to shrink and dont touch the thermocouple.If its 25 yrs old it will probably be the Housewarmer range.The best way of lighting it is to pull the bottom flap off,use a straw or a pen refill and stick a match in the end.Then push the gasvalve button and aim the taper towards the pilot.It should light but if it does go out after you have held the button in for 30 secs then it is either the t/couple or the pilot needs cleaning out.

Tony S
September 2008