Sorry to list such a basic question but... When I light my forge fire, to begin with the airflow seems ok, ( I am using a vacuum cleaner so far.) but after an hour or so there is no or little airflow and the metal doesn't seem to heat up enough. Every now and then I put the poker in and lift the coals and it helps 10%. Is there something I am doing wrong or maybe a vac cleaner just isn't powerful enough?

I think I hear a clinker in the fire pot.

When this happens root around at the bottom of your fire pot with your pocker and you'll find this gummy gooy blob of contaminates from the coal, pull it out and toss it aside and it should be flame on again for another hour or so

Hi Allen, What fuel are you using (sounds like coke) my fire does the same after a while and it is exactly what has been mentioned, impurities in the coke/coal that form a sticky paste similiar to melted plastic. I use a vacumm cleaner also and find it to be very suitable in supplying a constant air supply (have a airgate attatched) when I lose the airflow somewhat or the fire does not seem to be heating correctly I just open the airgate and stir the base of the fire and if I can, get rid of any clinkers I find, or just dislodge them to another area of the fire. You need a good fire in Ballarat,I lived there for 18years cheers Bully

The vacuum is likely a bit too powerful. Try a hair dryer or heat gun instead. I have used a vacuum myself and had to keep it off most of the time. I have a new forge now and the clinker breaker feature and ash dump prevent this problem. Fe-Wood is on the right track though, clinker and ash are the likely culprits.

Before you start poking around in the fire, shut off the air blast for a few minutes and let the clinker solidify, it is then far easier to lift out in a big lump (and maybe some smaller ones) rather than trying to do it when the clinker is molten when it just gets redistributed into the good fuel and leaves a dirty fire.

If you put a poker into the base of the fire and lever it up gently after you have shut the air off for a few minutes, you can usually see all the heart of the fire lift as one, this would indicate the size of the clinker in the base of the fire, and the fact that it needs removing.

I use John B's method regularly any time the fire isn't performing. Also any time I have banked the fire and shut off the air while I do other work, I will fish out the clinkers before I run air again. Keep a clean fire.

sounds like clinker to me too.. can't add to instructions already stated, but it happens to me too, I burn coal,