Can anyone recommend a reliable gasfitter in west Auckland?

I have a Vulcan Freeloader mains gas hot water heater and it is playing up.
It is an odd issue that I can't work out.

Main issue is that it is only heating to warm, not hot.

Mains gas is ON.
Pilot light is LIT.
Unit is heating water somewhat, just not to HOT.
Seems like the gas flame does not automagically come on to full when required.

Happened on Christmas day of course :)

Any suggestions welcome, thanks.

Cheers,
Joseph