Vauxhall Zafira heating

Could be heater flap /air mixing flap stuck or not operating .Could also check this suggested solution on same fault



Vauxhall Zafira Heater - no heat


Do you have air conditioning on your vehicle? If you do, then there is an
additional valve in the coolant circuit to the heater matrix. This valve
stops flow of coolant through the matrix when the heat control is set to
fully cold. It is a round disc shaped object, about 2" dia., with a single
vacuum pipe comingout of the top, and is mounted on one of the two coolant
pipes where they run through the bulkhead (engine side) and into the heater
box. Try disconnecting and plugging this vacuum hose and seeing if the
heater then works. If it does, then the vaccum control system for this
valve has a fault. If it doesn't, then either the valve is stuck or there
is a blockage or air lock in the heater matrix or pipes to it.