I have a bosch extra pump on mine when the original failed .works fine but have just wired in a relay to cut it out when the aircon comes on.
I did not realize that the pump and solenoid do not work with the ignition on you have to have the engine running. No good trying to fault find with your meter if the engine is not running.
Note the ECU switches live to the water solenoid and switches earth to the pump relay to work the pump. The ECU switches both the solenoid and the pump on and off to control the cabin temp.

 

The experience on my '03 is different. The heater pump is always on when the heat/cool control panel is on, which requires the ignition to be on. Key On, Engine off like they say. The reason it is "OK" to do is that the original pump is just a spinning magnet. If the water valve is closed, the impeller just stops, it does not keep spinning and make cavitation noises. To my knowledge, the pump is just on basically all the time with no attempt by the ECU to control its speed.

The water valve defaults open. The ECU controls the amount of hot water going into the core by PWM, effectively doing a controlled closing of said valve by switching the control current on and off for the desired duty cycle. It's documented somewhere, something about a long 6 sec cycle.

Not sure why you would want to stop the heater pump when the A/C comes on. What about a scenario where it is cold (you want the heat) but you have condensation on the windows (defrost)? The A/C works wonders under those circumstances. Then again, you live in the UK, what would I have to say about that that you would not already know?

Best of luck, keep us posted.

 

Mine is a 97 so maybe different ..the Bosch pump has no magnetic drive so I dont want it running when there is no water flow.
I think on mine when the temp reaches what has been set the water valve closes and opens again when the temp falls . Now when the valve opens the pump kicks in.

 

What model of Bosch pump have you fitted ?
The replacement Bosch pump recommended for the XKR intercooler system has magnetic coupling. In fact all 3 of the different pump models recommended do.
Though it must be better for the life of the pump if switched with the water valve like you have done.

From the Bosch literature:
Armature torque is transferred to the impeller wheel by means of magnetic connection through a permanent magnet coupling; this means that the pump motor will not burn out if the impeller becomes jammed.

 

Bosch pump is 0392020039 would be great if you could tell me if it has a clutch.
Its fitted in the inlet to the heater core.
Its worked fine in the winter for months but the complication is that I ( idiot) fitted a none jag relay in the pump slot and I think I lost the earth via the ECU. Maybe I did not as at that time I did not know I needed the engine running for the system to work. ( just tested with ign on)
I have a relay buddied up with the water solenoid to turn off the pump when the solenoid cuts off the water to the heater core.

 

Yes that pump has the magnetic coupling and is listed in the Bosch catalogue, the catalogue also shows a cutaway internal view showing the magnetic drive. If you are interested I have attached the Bosch pump catalogue.
I would leave your pump connections, that turn it on and off with the water valve, alone. I think that is an excellent solution and will increase the life of the pump.

 

Brilliant work stumpy and I see it is supressed inside too.
I had it on with the ignition 24/7 but in the summer it would have been blocked off most of the time.

Great job