Cheeko wrote:

Well hopefully that’s one less thing to think about 60s in started smoking 80s in stopped smoking was still running 😂😱 Thankyou very much for your help hopefully winter I won’t have a problem might go buy some spray for sake of £8 to test it properly Thankyou

Not so fast! You need it to be able to run right to the end of the 300 second test cycle.

When it starts up, the glow plug starts to heat up, then after about 20 seconds the fan starts up then at about 45 seconds fuel starts to flow and it should ignite. If a flame is detected, then the fuel continues to flow but if no flame, the fuel flow stops. The fan continues to run to purge the burn chamber and allow the burner to cool down. If you listen to it you can hear each stage in the cycle including the change from fan only to fan + combustion. Quite often that extra combustion noise drops out after 30-40 seconds, indicating that flame-detection has failed.

If it stopped smoking at 80s, that could be because it is very clean burning or because it has stopped burning and is on the fan-on, purge cycle. My FBH does burn clean, which can make knowing whether it is running or not difficult, but when I got the car at first I had to run the GAP-IID test cycle a number of times before it would run right through to the full 300 seconds, before that it would stop early.

If you use the GAP "Live Values" option you can choose to display the coolant temperature at the FBH and at the engine. This allows you to check that the FBH is indeed warming the coolant, as the coolant temperature at the FBH will rise faster than at the engine - if the FBH is working!