Potterton works for either water or heating but not both

[rediproof]

I have a Potterton Suprima 60L and it has developed a problem. The system works fine when either heating water or the central heating but does not do both at the same time. After a few minutes of firing I get the green flashing light.

Checked the system for air and bled radiators. Got a plumber out who replaced the pump, checked the 3 port valve head and flushed the system but still has not resolved the problem.

Anyone have any ideas?

 

[ianmcd]

forget your plumber and get a heating engineer out , it is your 3 port valve and not your boiler

 

[MANDATE]

Within the actuator head is a small pcb, its job is to produce a modified voltage which is not sufficient to drive the motor forward, but enough to prevent the motor from unwinding.
2 micro switches create 4 sets of contacts.
1 of the 4 sets feed this pcb, so either the contacts are dirty/burnt and no power is getting to the pcb and it can't do its job. Or the pcb itself is faulty.
Changing the actuator head is best option. You get all new motor/micro switches.

The other contacts relate to:

powering the motor/valve to mid position on the valves white wire.

powering the motor/valve from mid position onwards by the valves grey wire

diverting power from feeding the pcb (not needed when in CH only position) and allowing power from the valves orange wire to feed the boiler/pump