Heater not hot as it should be

Rad coolant fan not cutting in too soon ?

its working like this without the rad fqn working

Just about the only things left would be a blocked heater matrix core or a weak coolant pump.
An old trick for a blocked core was to reverse the hoses,
effectively back flushing the core.
And the remedy for a weak pump is replacement.

it was reversed flushed till clean water came out all the heating system pipes are hot,it it had a week pump id have thought it would over heat

problem solved took heater matrix off and flushed it in the bath more pressure than a hose plpe and a lot more gung came out also put in caustic soda and even more came out