Boilermate 2000 Hot water Ok - but No heating.

I have a Boilermate 2000 with an Ideal ICOS Boiler.

I have hot water but the heating is not working properly.

The Domestic hot water is hot.
The upper two horizontal red LEDs on the panel are on as is the red LED word "On". The lower two green LEDs are illuminated.
The cupboard with the Boilermate is warm, (good for drying clothes).
The expansion tank is full and the water in the expansion tank is warm.
The pipes on the pump supplying the boiler is warm/hot on both sides.
When running DHW the 3rd (lower) horizontal red LED comes on and the right hand DHW pump runs.
The clock on the panel is set to 1. Timing is controlled by a timer at the room thermostat in the hallway.
I have checked all 3 pumps spin freely.

When switching the heating to on, thermostat up full, (It clicks on and off ok) the 3rd (Upper) green led comes on.
The middle pump runs, then the pipe both sides of the pump get warm/hot.
The radiators warm up but after just two or 3 minutes the pump stops, The upper green LED goes off.
After that the heating does not come back on. The middle (heating) pump gets quite warm/hot to the touch
If I leave it and I try again, say the next day, when the heating is cold, then when I turn the heating on, the pump will run again for a
couple of minutes and the radiators will warm up. After that, it goes off again, but does not restart, as above.

There may also be an issue with the boiler. I do not know if this is cause or effect with the heating problem.
When switching the boiler on, it will run for a few seconds. The status is Letter C and burner light illuminated.
However before it would go to status letter "O" (standby) and then fire up as demanded by the Boilerrmate.
Now it does not go to standby. The letter "c" (running) is on all the time and the burner light is flashing.
Every now and then the burner will come on. There is a sort of banging / Knocking / gurgling noise coming from the boiler when it is running and the burner is on.

Any help or ideas would be appreciated. Also does anyone know an experienced GLEDHILL ENGINEER in the North East near Sunderland or Newcastle.

Thanks, Cal.