Help needed on central heating problem

[Oakwood109]

Evening gents

I have a Worcester green star ri controlled by a Honeywell st9420c controller and wireless thermostat

All working fine this morning now when home from work I’m getting no heating. The light is on on the controller and the digital thermostat is showing the fire symbol but there’s no heating working at all

Hot water is heating up apparently fine and the boiler will periodically fire up and then stop again about 10 seconds later

Any ideas? Had a new grundfos pump and switch fitted 18 months ago

Thanks a lot in advance

 

[king of pipes]

Batteries in the stat ok ?

 

[Oakwood109]

Seem to be mate. Will double check
[automerge]1574803344[/automerge]
Yep changed them and still the same

 

[king of pipes]

Do you have a hot water cylinder and zone valves as below ? It may be a faulty head on the heating valve it may be possible to lock the head open its a common fault the motor may be burnt out or the linkage worn so not triggering the micro switch when it moved over . Kop