boiler will not stay alight!!

[dazzatay]

I have a very old (20+ years) Thorn M30/42C Boiler that won't sta

alight. The pilot goes out every day. I put the top dial on to only (1-10) as a plumber once told me that it overheats and switches itsel off. Another plumber told me that the pilot may be getting blown out b air coming through the flue. Whatever it is it's annoying. As you ca imagine getting up in the morning to no hot water and heating is pain. Does anyone have any ideas how to solve this problem or am i looking a a new boiler

-- dazzatay

[Set Square]

I presume that it's a boiler with a permanent pilot light?

As well as being there to light the main boiler when required, the pilot light is part of the safety system. If it goes out, the flame failure device shuts the gas valve and prevents any gas from escaping.

The flame failure device is driven by a thermocouple which is heated by the pilot flame. If the pilot keeps going out, it usually means that the flame isn't strong enough, or that it's not correctly directed towards the thermocouple, or that the thermocouple itself is flakey.

Make sure that there's no crud in the pilot jet, and that the height of the pilot flame is correct. There's often a separate little governor to allow the height to be adjusted. Make sure that the thermocouple is in the blue part of the flame. If it still goes out after doing all that, try replacing the thermocouple.

[Andrew Mawson]

itself

Has the thermocouple been changed - this would be my first suspect? This is the safety device that pokes into the pilot flame and generates a small electrical current to hold the gas valve open. If the pilot flame fails (or the thermocouple fails) the gas valve shuts down and gives you your symptom. They do age as they erode in the hot flame and yours may be 'just on the edge'. An alternative cause is that the pilot flame jet may be slightly blocked and hence too small a flame to adequately heat the thermocouple.

AWEM