Heat Stops When Stopped?

I think the antifreeze level is low, before starting in Morning, open hood and remove radiator cap, not the plastic overflow container, the radiator cap. if low ----fill it up.

it was low from long term neglect or has a small leak somewhere.......... so check this again in 2 weeks.

when driving the car the engine turns much faster and makes the

water pump spin faster to enable the antifreeze to flow about the engine , hoses and heater core (where the heat comes from)

when the fluid level is low and the engine is idling at the stop light, the water pump is not spinning fast enough to pump the low or " limited "amount of fluid to the heater box.

check your levels in the RADIATOR. Only open the radiator only when the engine is COLD. The reservoire may be full, but may not be drawing fluid to the radiator.

sounds like your water pump is going bad or a blockedge