Problem draining the pulsacoil 2000

Hi, I tried to drain the main tank, i connected a hose to the drain outlet and opened the valve,, but i could not get it to drain, i even blowed into the hose to see if it was blocked but that never worked either, have i missed something?? what is the correct procedure to drain it off so that i can change the imersion heaters>??

Thanks: ScrumpyJack

Its the drain off cock.
They are a lot of trouble.
In all forms of systems.
You have 2 drain offs
1 above the pump.
Try that
If not get a new doc or look at one ( undo it)
You will see what the problem could be.
Washer stuck but not in your case.
Would say the jumper and washer is stuck.
If not too hot you can un do the gland and undo more.
But experiance is the key here.
Mike

Thanks Mike,, these systems are new to me, If the second drain point is also faulty can the tank be syphoned off from the top?
The tank is cold due to both heaters being knackered,, I only had chance to have a quick look at it when it failed to drain, but now the work has been approved by the landlord i will be returning once the new heaters have been delivered,, I have taken the advice you have given elsewhere on this forum and bought original Gledhill parts even though expensive.
Also the wiring seems to have been switched around at some point in its life so one heater was always on and the boost switch is only active through the night when the eco7 kicks in..! I guess most people scratch there heads when they first see one of these systems!