Car heater blowing cold air sometimes
 

This happens once in a while. Like today, I started the car, put the heater on and drove for a few miles, the air was still cold, then I noticed my engine temperature go up and it went into the red, so I pulled over and switched of the engine. When I switched it back on after about 10 minutes, hot air started blowing and the engine temp remained at the normal level. Any suggestions as to what is happening? My coolant is full. I've got a 2002 Honda Accord

Check the coolant level in the radiator. The plastic tank can be full but not the radiator and engine where it matters. If that's what happened, it could be the radiator cap or the hose to the tank.

I had a similar problem, which turned out to be a bad a faulty water pump?

How much did it cost you to put a new water pump?

cost £110 including timing belt change at the same time