Could be, how many miles has the car done?

Look in the expansion tank when it's running, and see if blipping the throttle produces a nice squirt from the highest hose attached.

Thermostat is most likely.

car has done 105,400mls.

will check the tank in the morning.

if it was the thermostat, would the temp gauge read as normal?

33 minutes ago, craigsvrs said:

if it was the thermostat, would the temp gauge read as normal?

 

Modern temp gauges stabilise at a wide temp range, so it could still be running a bit cold but show normal on the gauge.

ok, so that may be the cheaper place to start.

just been out in car today.

car temp gauge got up to halfway pretty quickly, warm air out of heater but as soon as your speed drops i.e in traffic it starts to get colder.

only seems warmish while moving, never red hot.

checked coolant level, ok.

heater control/flap moving ok.

had car to my local garage who carried out a flush of coolant system including heater matrix, lots of sludge came out apparently.

I must admit I have never had the coolant changed since I have had the car.

heater is warmer now. will find out in the morning when going to work in frosty conditions.