I have water leaking from the engine, but don't know where from. The radiator has been changed the water tested for emmissions, pressure tested and still water is leaking. The heating blows hot when under pressure but cold when stationary - can you please help me. The car is a rover 45 02 plate 1.6

Get a cooling system pressure test done. Then you'll know where the coolant is leaking

look for a leak from the drain hole under the pump housing, if no leak not a water pump
take the car to a radiator specialist shop and have a coolant pressure test done to determine where the leak is
if it has plastic tanks for the radiator , they split with time and leak under pressure and a pressure test will reveal exactly where the leak is unlike a guess

Have a coolant system pressure test done. Have a compression test done. Either one will show gasket or cracked head.

the code is for coolant leak large. Check coolant level and top off.
check the oil for moisture.
pull the plugs to see if any are steam cleaned.
either one could indicate a bad head gasket or worse damaged head.
Check to see if any new hoses have been added. tighten clamps if needed.
look on engine block for any puddles where coolant could be leaking.
pressure test coolant system and check for leaks.
If you can smell coolant inside the vehicle check the heater core.
lastly have an emissions test run with the radiator cap off and at running temperature. Start vehicle with cap off to avoid spray of hot coolant. This tests head gasket and cyl head for leaks.

see this causes and fix it. God bless you
Water pump -- A bad shaft seal will allow coolant to dribble out of the vent hole just under the water pump pulley shaft. If the water pump is a two-piece unit with a backing plate, the gasket between the housing and back cover may be leaking. The gasket or o-ring that seals the pump to the engine front cover on cover-mounted water pumps can also leak coolant. Look for stains, discoloration or liquid coolant on the outside of the water pump or engine.
Radiator -- Radiators can develop leaks around upper or loser hose connections as a result of vibration. The seams where the core is mated to the end tanks is another place where leaks frequently develop, especially on aluminum radiators with plastic end tanks. On copper/brass radiators, leaks typically occur where the cooling tubes in the core are connected or soldered to the core headers. The core itself is also vulnerable to stone damage. Internal corrosion caused by old coolant that has never been changed can also eat through the metal in the radiator, causing it to leak.
Most cooling systems today are designed to operate at 8 to 14 psi. If the radiator can't hold pressure, your engine will overheat and lose coolant.
Hoses -- Cracks, pinholes or splits in a radiator hose or heater hose will leak coolant. A hose leak will usually send a stream of hot coolant spraying out of the hose. A corroded hose connection or a loose or damaged hose clamp may also allow coolant to leak from the end of a hose. Sometimes the leak may only occur once the hose gets hot and the pinhole or crack opens up.

If your car passed the pressure test, then there must be no leak in the cooling system. It can only come from the overflow reservoir.

You can change the water pump by doing these steps:

• With the engine off and cold, o pen the hood and locate the vehicle’s radiator and water pump.
• Remove the radiator cap.
• Install a pressure tester on the radiator. Apply the pressure indicated on the radiator cap or in the owner’s manual.
• Inspect the water pump for leaks. Remove the pressure tester.
• Place a drain pan under the radiator. Open the drain valve or remove the lower radiator hose to drain the cooling system.
• Remove the drive belts or serpentine belt.
• Remove any hoses connected to the water pump.
• Unbolt the water pump from the engine. Remove the water pump.
• Using a gasket scraper, clean the mounting surface on the engine block.
• Install a new gasket and attach the new water pump to the engine with the original mounting bolts. Tighten the bolts to the manufacturer’s specifications.
• Re-install any hoses and belts that were removed.
• Re-install the drain plug or lower radiator hose.
• Refill the radiator with a 50/50 mix of coolant and distilled water. Pressure test the cooling system and check for leaks.
• Check and fill the overflow reservoir with coolant.
• Leave the radiator cap off and start the engine. Idle the engine to remove trapped air from the cooling system. Add coolant if necessary.
• Install the radiator cap.
• Road test the vehicle and monitor the temperature gauge. If the vehicle runs hot, there may be an air pocket in the cooling system. Allow the engine to cool off and add the necessary coolant.

All car cooling systems have at least 10lb pressure, check with your manufacturer on your car's radiator pressure cap or local parts supplier. If pressure is alot more then I would suspect a leaking head gasket.

Easiest test for the obvious leaking head gasket is when the engineis cold / remove the radiator cap and fill right to the top with water and crank / start engine. If you see a mini "guyser" of water come out then head (S) need to come off.

You haven't mentioned whether its actually losing . using water??

Check your radiator pressure cap see if theres too much pressure in it. If not that which I think it is, your thermostat may be stuck closed.

The water (coolant) in the expansion tank will rise and fall with the engine temperature. What the expansion tank does is collect and return coolant to and from the engine. When the engine warms up the coolant gets hot, builds up pressure and opens up the radiator cap. The coolant then goes into the expansion tank. Now when the engine cools down the pressure drops in the cooling system and the pressure drop (vacuum) pulls the coolant back into the engine via the radiator cap. The radiator cap allows the cooling system to build up pressure and by doing so increases the boiling point of the coolant, but when that pressure exceeds the caps rating the cap opens and the coolant goes to the expansion valve. The cap has another part to it that when the engine cools down and a partial vacuum is created in the cooling system a "valve" in the radiator cap opens and allows the coolant to be drawn back into the engine. I would look at your radiator cap to see if any gunk or build up is on it, and check the rubber gaskets for cracks. It's easiest just to replace the cap because they are inexpensive and easy to replace (2-10 dollars). The expansion tank should have two hoses on it. The one on the bottom comes from the radiator and the one on the top (possibly part of filler cap) runs down and is open to the ground. That way if it is overfilled or becomes overfilled it will slowly leak onto the ground. When and if you change your radiator cap, make sure the engine is cooled down, remove cap and start engine and turn heater to full blast, full heat. Leave the cap off and let it run until engine warmed up. This should burp out any air pockets that may have happened when coolant was changed. Also top off the coolant in the radiator while it is running. Hope this helps and good luck