When you say intermittantly is there any pattern to it? If it gets hot on a low fan setting, then when you turn the fan up it cools down I sugest you should suspect the heater matrix is blocked. If this is the case add a bottle of fernox central heating cleaner to your cooland and run it until the fan kicks in. Then allow it to cool and drain the coolant. Now disconnect the heater in and out pipes and flush the matrix through with a hose pipe on full power.

Finally reconnect the heater and refil and bleed the cooling system.

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