Glowworm Ultimate 30FF Cuts out when heating is called

[PIC110]

Hi,
Heating started to play up on Saturday morning on first frosty cold day of the year.
No neon lights on the PCB. At that time, both heat and water called for.
Had a heating engineer out who suspected was PCB.
However, I noticed that when no call for heat or water, neon lights all on.
The boiler would fire up as it should. As soon as a call from programmer for heat and or hot water, the boiler cuts out and all neon lights go out.
I spoke to engineer again and he then suspected could be faulty motorised valve head. He came back next day and set the motorised valve from Auto to Manual and that now pumped hot water to all the radiators.
Programmer is a Landis & Gyr RWB9.
I think it is a fully pumped system. Boiler in garage with 2 frost stats. 1 on pipe above boiler and other on the wall.
Thermostat in the hall as well.

Any ideas on what could be the cause.
Thank you.

 

[Armo74]

If it is working in the manual position then the motor has gone and not moving the valve over when heating is called for, as the valve moves into position it activates a microswitch which then fires up the pump and boiler.

 

[twgas]

Can you explain the bit about the boiler firing up as it should when there is no call, obviously it shouldn't.

 

[PIC110]

On the programmer, both water and heat in the Auto mode, no call for heat or water, boiler is lit and running.
I agree that in this configuration that nothing should be on and I have noticed before that boiler has been running on its own this way.

Could the programmer be faulty as well?

With regard to the motorised valve, if was faulty, please explain why the boiler goes off completely including the neon lights so that I can understand more.

Also, apparently the motorised valve is in 2 parts, the head and the valve.
I believe the engineer is changing the head bit.
Thanks.