Honeywell DT90E thermostat

[bilco_21]

Hi guys, I've just up graded my Honeywell dial thermostat to a DT90e digital type. The programmer I have is the Honeywell st9400c. When the programmer turns the heating off at say 10pm for the night the thermostat still stays on. This in itself isn't a problem but in the middle of the night when the temp drops it calls for heat and keeps clicking on and off, without the boiler coming on as its off on the programmer. Is this correct or should the stat go off with the programmer or if not is it safe for it to operate without the programmer on????
Will

 

[bilco_21]

This also means that I can't use any of the optimum start or stop features as the stat never goes off with the timer! I have only used the live and S/L wires in the stat should I have put the neutral in terminal C???

 

[doitmyself]

This also means that I can't use any of the optimum start or stop features as the stat never goes off with the timer! I have only used the live and S/L wires in the stat should I have put the neutral in terminal C???

The DT90E doesn't have optimum start and stop; you need a programmable stat for that, e.g the CM901 or CM907.

Do NOT connect neutral to C; you will blow up the stat if you do.

The stat will click on and off overnight, but this will be ignored as the programmer is off. The same thing would have happened with your old mechanical stat, i.e it would have been calling for heat, but it wouldn't have been so apparent.