Boiler not starting from one of four Digistat feeds

[stuart st paul]

House is in 4 x sections. 4 x Thermostats. I not starting the boiler. Have switch out the broken section to another section and it starts that other good section. Have put good pair on bad section, no start. Have pulled out the mass of wiring and checked all connections are good. They are. Have poked them about. No change. Have listen to valve and it appears to give sound. Stumped? Ant ideas.

 

[Brambles]

Check the wiring continuity on the errant circuit. Pay particular attention to the valve end switch - it must close when the valve opens