Grate glow fire problem?

[mummynun]

I have a grateglow gas fire and had the thermocouple replaced about 2 months ago. Now, when lighting it (with a match as igniter busted) the gas only seems to allow a very small blue flame and therefore the little cap thing on top which distributes the flame 3 ways doesn't have enough coming out of it to stay lit when I let go of the button underneath. Its almost like the gas isn't strong enough to make a big enough flame. If you can offer any advice it would be greatly appreciated. I know if its not an easy fix I will have to get a gas safe engineer out but were freezing and its 8.30pm on a Saturday night.
Thank you x

[buildersmate]

The typical purpose of the thermocouple is a safety device such that if the flame is extinguished, the main gas supply is cut off.
When one lights the pilot, the small flame warms the thermocouple up which transmits a message back to the main gas valve to say that all is well and the main supply can go on.
It sounds like your fire is not getting to this stage - and it is typically caused when the thermocouple is faulty.
Sounds like a Gas Safe technician job.