Rads hot: water not.

[nedflanders]

Hi, I have this rather ancient gravity/pumped CH system, using a Baxi Bermuda LFE5 Super back boiler operated through a room stat. No stat on the (indirect) HW tank.
Question: The CH works, but doesn't heat the water in the tank at the same time. Can anyone please explain why?
The controller is a Drayton Tempus with the Boiler and the Pump wired together via the timer and room stat.
Yesterday I disconnected the Pump wire and switched on, and the pipes to the coil heated up, so I guess there's no blockage.
Is the pump nicking all the water for the rads?
I'm sure it used to work!
Any help would be greatly appreciated.

 

[namsag]

The first thing to check on a gravity system when no Hot water is the little header tank is actually full and letting water into the system

 

[nedflanders]

Hi, Namsag. Yes the header tank's okay. With the pump disconnected (unwired) the boiler heats the water in the tank.
I was under the impression that the system should heat the water while it's heating the rads; in other words, CH on, hot water automatically gravitates up to the HW tank as well.
Maybe not.
Thanks anyway.