honeywell st9400c

Thank you for taking the time to read this. We have recently moved into a new house which has an Ariston Clas HE system evo boiler (without clock) operated by a Honeywell ST9400C timing control with separate walled mounted thermostat. Each of the three items appear to be operating correctly...

Hello A few years ago I replaced (and rewired & changed back plate) a Honeywell ST7100 with a new Honeywell st9400c for a gravity system. The reason was that the old controller was coming ON at random times (both HW and CH) when it should have been OFF. However, this problem has persisted for...