Thermocouple failure?

[Rosey]

We have a Broag condensing boiler of about 15 years old called a Seagold. Every so often - sometimes after just a couple of weeks - the pilot light refuses to stay on. Replacing the thermocouple seems to fix it, but then it goes again!
I am wondering if we should use a different thermocouple, maybe there are heavy duty types or could there be something causing it to short out in some way?
We use a Honeywell Q309A 2788 900mm if that means anything!
Before it gives up completely, the boiler cuts out and has to be fired up by holding the button down for up to a minute, sometimes longer (after igniting) before it will stay on.
Many thanks to anyone who could give us some ideas on this.

 

[ChrisR]

First try a genuine Honeywell themocouple. The cheap universal ones dn't last too long. You can get Nickle plpated ones for LPG which might last longer on natural gas too.
Have you had the boiler serviced - pilot flame could be a bit too big/hot. Sometimes a new pilot injector is needed on older boilers - though I've never come across one of yours!