We have been asked to look at the above unit. At start up the backboiler goes through the ignition sequence and fires up. After 10/15 seconds it shuts down and again goes through the start up sequence (this repeats). I believe it may be the thermocouple ?. The problem is we do not have a manual for this unit to show how to remove the fire and allow access to the boiler after turning off the gas supply and disconnecting the gas connection from the fire. Can anyone help? The unit is approximately 7 years old and cannot find any technical manuals on it