Bob Minchin wrote:
kennygw wrote:
Hello I hope someone can help with this one.
I have an old Potterton fireside black beauty 35/51 back boiler.

until this morning it was running fine. It flamed up fine and the
heating/water came one fine. after it bit it turned itself off, and the
pilot
light went out.
I turn the starter vale to off and left it to cool down.
when I went back to it to relight the pilot light after about 20
minuets. It
relight fine I turned the starter vale back to on. After about 20
seconds the
was a hissing sound then a clicking sound and the pilot light goes out.

I gave it all a good clean with vacuum cleaner and air duster.
It does the same, the pilot light come one fire time very time. The
flame
look nice a blue and is one flame.
If I turn the heating and water on before I light the boiler it will
flame up
fine and run okay for a bit.
It looking like it get to where it will flame down in normal operation
then
after about 20 seconds it stars to hiss then the pilot light goes out.
Anyone got any idea what is up with it?



Highly likely that you need a new thermocouple. they are pretty
universal and readily available in a kit with a number of different
accessories.
EG
http://www.toolstation.com/shop/Heat...ocouple/p64067

Screwfux will have one too.

In our boiler, the top socket crusts up (and points the pilot flame in
the wrong direction) sooner than the thermocouple itself packs in. I
don't know if the OP's has anything like that.